# DIY Drop Checker



## hoppycalif

It is quite easy to make your own "Drop Checker" or CO2 Indicator from acrylic sheet. The object is to have a small device that holds a few ml of water/indicator solution under the water line of the tank, so there is an air gap between the tank water and the indicator solution water. The commercial versions of this range from the elegant ADA glass unit, which is currently out of stock, to a much cheaper imitation ADA glass unit from Hong Kong, to a Red Sea plastic unit which is still cheaper. All do the same job. Two of the commercial versions are the imiitation ADA unit:









and the Red Sea unit:









Both are available on ebay at: eBay: Type2 Co2 Drop Checker-monitoring proper dosage of CO2 (item 250038130859 end time Oct-18-06 09:05:18 PDT)
and eBay: CO2 Indicator Red Sea Real Time CO2 Monitor (item 300036151186 end time Oct-14-06 09:48:10 PDT)

The easiest way to DIY this is to use all straight lines and rectangles, and make it from acrylic plastic. I made one a couple of years ago, but hadn't figured out how to effectively use it so I tossed it. Here is what it looks like:









All of the pieces of acrylic have to have squared edges, and the pieces that establish the thickness of the device should be cut from a constant width strip. When glueing these together, remember, the assembly has to be air and water tight, and any smearing of the cement makes it hard to see the color of the indicator solution. For an indicator solution you can use the solution from an Aquarium Pharmaceuticals pH test kit, or any other test kit that gives yellow at pH=6 and blue at pH=7.2 - use at least double the number of drops of indicator solution as the kit says to use, to get a more intense color. (Using even 4X the recommended number of drops doesn't change the test reading, only the intensity of the color.) To use this see: 
http://www.aquaticplantcentral.com/...it-work-ada-glass-dropcheck-3.html#post236934


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## elaphe

Hoppy,

Thanks for all the reviews and being a guinea pig for this. 

I couldn't resist anymore. I had to order one of the ADA knockoffs from Ebay.

One question. Does the dKH of the indicator solution need to be 4 dKH or should it be whatever the tank water is?

Thanks again,
Brian


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## hoppycalif

The reason for setting the KH of the indicator solution to 4 is so that with 30 ppm of CO2 the indicator color will be green, and an unequivocal green. That gives the maximum accuracy. If you had a lower KH, the 30ppm color would be near yellow, almost impossible to judge, and if you had a higher KH, the color would be blue green, again very hard to judge. Actually, any KH that is within .5 of 4.0 will work, but 4 seems to be just about the perfect KH. Since it is easy to get the KH to whatever you want it to be, as accurate as you want it to be, why not shoot for 4.00 KH? (You can even use 10X the usual water sample size, so that each drop of KH solution will equal .1 degrees of KH. I used 4X and could judge it even closer by noting how nearly each drop came to tipping the color over to yellow. (I use AP test kits)


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## elaphe

Hoppy,

Thanks for clearing that up. This seems like such a handy device. I can't wait to get it in the mail!

Thanks again,
Brian


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## hoppycalif

Yesterday I cleaned up the GDA, changed about 90% of the water, tossed most of the BBA infested plants, bleach dipped the anubias and java ferns, etc. and I took another photo of my "drop checker" in action:










Notice that it is running a good green color, meaning I have 30 ppm of CO2 in the water, early in the morning. I love that little bit of glass!!


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## quatermass

My glass Drop checker from Aqua Essentials in the UK (Aquili Permanent C02 test at £13) goes green when its around 15ppm.

Aquili Permanent C02 test [25265] - £12.99 : Aqua Essentials

Isn't 15ppm the right amount of CO2?


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## epicfish

30 ppm = optimal.


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## hoppycalif

It is hard to know what the best ppm of CO2 is, since the numbers people use are all based on measuring pH and KH of the tank water, which is not an accurate method, due to the other things besides CO2 that affect acidity and alkalinity in our tank water. You can choose the ppm of CO2 you want the indicator to be green at, by adjusting the KH of the distilled water in the bulb. I picked 30 ppm believing that to be at least not too much. For that I used KH=4.0 in the bulb. I am thinking about raising the KH to maybe 5 later, to get green at 40 ppm, and if that is still ok, going to KH of 6 to get green at 45 ppm. This would be a way to finally determine what the "best" ppm of CO2 really is.


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## Gatorguy

So what are you doing to make the "solution" 4 dKH? 

So you want the "solution" in the drop checker to be 4 dKH, then you add a pH regeant so that you can "see" the pH change in the solution as it is exposed to more or less CO2 that is diffused from the aquarium through the air gap and into the solution? 

I must be missing something. 4 dKH and "green" (my test kit is pH 7 at green) would only be 12ppm. Where am I going wrong?

I'm probably fixing to order one of those drop checkers from eBay. Why not?


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## hoppycalif

Here are the color charts for the three commonly used pH test kit reagents. For the top one, it is yellow at pH of 6.0, blue at 7.2, and green (the middle) at 6.6.


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## wantplantsnotwork

Can someone please explain (in steps for this short bus rider!) exactly /how this works / how to use it? 
Does that green test solution ever migrate into the tank? If it ever did, what happens?
Thanks!


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## hoppycalif

This works because a sealed container of air in contact with water will reach an equillibrium amount of CO2 that is at least proportional to the ppm of CO2 in the water. So, two containers with their water in contact with the same sealed container of air will reach the same ppm of CO2. The "drop checker" has distilled or DI water in it, with a known KH obtained with bicarbonate only - no other source of alkalinity, and no source of acidity. That makes the equation that is behind the pH/KH/CO2 table work correctly (see Chuck Gadd's website). So, if we can measure the pH of that little bit of water in the "drop checker", and we can, by using a pH indicator solution, we can accurately calculate how much CO2 is in that container of water, which will be the same as is in the tank water, since they are connected with a sealed air column. At KH=4, and 30 ppm of CO2, the pH will be 6.6 which turns the bromothymol blue indicator, used in almost all pH kits, green. So, green means you have the right amount of CO2 in the water, and yellow green means you have too much, while blue green means you have too little.

There is no way for the indicator solution to migrate to the tank water, since there is an air gap separating it from the tank water. If it did get into the tank water, it would be about 4-8 drops of a 4% sodium hydroxide in water solution with a little bit of bromothymol blue dye in it. It wouldn't be desirable to have it mixed into the tank, but I doubt it harming anything if it were mixed in.

So, to use this:
First, get some distilled water from the grocery store.
Using clean glass container, pour about a cup of that water into the container.
Next, add a very small amount of bicarbonate of soda - baking soda - Arm and Hammer soda, etc. to the water and stir it up with a very clean stirrer.
Test the KH of that water with your test kit.
Most likely it will be a higher than 4 KH. So, add some more distilled water and repeat the test. (If the first KH comes out to 8 degrees KH, double the amount of water. If it is 6 degrees of KH, add 50% more water, etc.)
When you get close to 4 degrees KH, repeat the test using twice as big a water sample in the vial as the kit calls for, then count each drop of KH reagent as being half the degrees of KH that the kit normally says - for AP test kit, that makes each drop equal to .5 degrees KH. I found I can get very near "exactly" 4 degrees KH by doing this carefully.
Use a syringe to squirt some of this 4 degrees KH water into the bulb of the "drop checker". Fill the bulb about 2/3 full of the water.
Add a few drops of your pH test reagent - use enough to get a strong blue color, but not so much that the water becomes opaque with the blue dye.
Use the suction cup on the "drop checker" to suspend the device two or three inches below the tank water surface, with the "horn" of the "drop checker" pointing down so it traps air in the horn.

After a couple of hours or so the color of the "drop checker" fluid will be at about the equillibrium color, and that should be green if you have 30 ppm of CO2 in the water. If the color is yellow, you have at least 70 ppm of CO2 (and your fish are in serious trouble!). If it is blue, you have about 10 ppm of CO2, which is not nearly enough.


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## wantplantsnotwork

Thanks for taking the time to get that out Hoppy, I appreciate it!


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## Gatorguy

Yeah Hoppy, thanks! That is what I was fishing for in my last post. Wantplants asked in a better way than I.

Thanks!!


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## Gatorguy

*Another Question*

What is the difference between type 1 and type 2 on the knock off eBay drop checkers? It looks like the "bottom" bell is a different shape. Is it just an asthetic thing or is there a functional difference between the two? There is about $2 difference between them.

Also, I just noticed they have a different style yet. Look at this eBay: NEW!! Co2 Drop Checker-monitoring proper dosage of CO2 (item 250039658709 end time Oct-23-06 08:45:25 PDT)


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## hoppycalif

Functionally, they have to all be the same. But, esthetically there is a difference. I think, from looking at the photos, the "type 1" is a more direct copy of the ADA unit, while the "type 2" is produced by a different glass blower, and less effort was put into matching the appearance of the ADA unit. The teardrop shaped one is still another glass blower's interpretation of the idea. It looks very good, but I doubt it having as fast a response to changes in tank water CO2, since it seems to have a much smaller tank water interface (no "horn" to increase the surface area of the tank water being interfaced.) That last one would be much easier to load with water and indicator solution, and might satisfy some people much more for that reason. It is pretty hard to get the water and indicator into the "type 1" verson, and nearly impossible without a syringe with a bent "needle".

What is encouraging about this is that apparently this fellow in Hong Kong is selling these well enough to branch out into other versions. Maybe our discussions involving ppm of CO2 in the water will become more meaningful as more people use these.


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## turbowagon

ok, that is officially the coolest invention ever. Definitely gonna order one! Thanks for the link!

- Joe


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## elaphe

I got mine installed and working. The hardest part was getting the RO/DI water to 4 dKH. I think I spent about 1 hour doing this (add baking soda, more baking soda, more water, etc...). It was a little difficult getting the water/indicator in until I realized that the old pipettes from Seachem Flourish bend right around that tight curve and squirt it right in the bulb.

It is a very cool device that gives you a good indication of the CO2 levels at a glance.

Thanks for being the guinea pig and trying this out for us \\/ .

Brian


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## hoppycalif

elaphe said:


> I got mine installed and working. The hardest part was getting the RO/DI water to 4 dKH. I think I spent about 1 hour doing this (add baking soda, more baking soda, more water, etc...). It was a little difficult getting the water/indicator in until I realized that the old pipettes from Seachem Flourish bend right around that tight curve and squirt it right in the bulb.
> 
> It is a very cool device that gives you a good indication of the CO2 levels at a glance.
> 
> Thanks for being the guinea pig and trying this out for us \\/ .
> 
> Brian


Thank you for biting the bullet and trying it too. I am now running mine with 5dKH water in it, so green means about 40 ppm of CO2. After a week or so it is still doing just fine. Apparently 40 ppm does not bother the fish. I hope a lot of us start using this little gadget, so we can find any problems there might be with it.


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## MrSanders

I ordered some stuff from big al's the other day, and i went ahead and got one of the little red sea, chepo deals.... Not aspretty but appears to be the same thing  Just to mess around with and see how it works out, this this one will work as well as the much better glass looking ones?


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## Gatorguy

I ordered mine a couple of nights ago, so I will have it up and running in a week or so hopefully.


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## LindaC

I'll be interested in hearing from more and more people on how these drop checkers work. I'm also thinking of ordering one but may wait a bit longer.


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## schaadrak

For a faster response time, couldn't you hook up a _small_ air pump to pull air from inside the checker and into the water in such a way that it bubbles back into the checker?

I'm not sure if the diffusion times for CO2 from water to air would be enhanced enough to warrant going through the trouble, but I thought I'd just throw it out there.


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## Gatorguy

Ok, that signature file got me intrigued. I think George Bush would classify that as "fuzzy math".

First, I have no idea where the 390.6 miles³ came from. Please help me out with that. Volume by definition is length x width x height. I see a width, I see a height, but I see no length. So how did we end up with 390.6 miles³ as a volume? And what is multiplied by what to yield 5.75 x 10¹³ ft³?? (390.6 x 5280³ = 2,062,368,000 ft³)

If we _assume_ 5.75 x 10¹³ ft³ as the total cubic feet of the canyon, given an average width of 6 miles and given an average depth of .3 miles, the length would have to be 217.0169 miles.

As taken from the National Park Service and also listed at The National Park Foundation, the canyon is 277 river miles long, an average of 10 miles wide, and a maximum of 1 mile deep. Multiplied out, that is 4.07738327 x 10^14 ft³ or 81,547.67 ft³ per person. Given an 8 ft ceiling height, my new house in the Grand Canyon is 10,193 ft² (Sign me up!). Of course, I will have no yard and no roof above my flat 8ft high ceiling. I probably won't even be able to open my frond door due to the neighbor back wall being shoved up against my house. Oh well, you can't win them all!


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## elaphe

OK, I've been running this for a week now. I love it! At first I set it up with 4dKH. Today I cleaned it out and made a 5 dKH so that I can bump up my CO2 up to around 40ppm for some algae issues (along with Excel).

Once it's in the tank and working, it really doesn't take more than a hour to start to see the color change. 

When I first mix it up and install it, the solution is dark blue, and it takes a couple of hours to get down to a green or yellow color. After that, it seem to respond fairly quickly.

This is a great little gadget.

Brian


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## hoppycalif

I'm still very pleased with mine too, but the same bubble rate entering the tank seems to take longer to change the indicator color to a good green. I can't see what, if anything, has changed, but now I get to green in mid afternoon or later, where as I recall it was early afternoon before. My indicator KH is 5 dKH too.


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## Gatorguy

How long is the solution supposed to last in the drop checker? Does it "wear out"?


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## elaphe

hoppycalif said:


> I'm still very pleased with mine too, but the same bubble rate entering the tank seems to take longer to change the indicator color to a good green. I can't see what, if anything, has changed, but now I get to green in mid afternoon or later, where as I recall it was early afternoon before. My indicator KH is 5 dKH too.


I don't have this problem since I'm running my CO2 24/7. It is only slightly greenish/yellow in the morning. About an hour or so after the lights come on it's nice and green.

One thing that I do notice is that with all the green plants in my tank the color seems to look green. To get a really good reading I have to put a piece of white plastic behind it to actually see the color. I may need to move it directly under my light. Right now I've got it more towards the front of the tank?

It may not be exact, but it seems to do the trick.

Brian


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## MrSanders

> One thing that I do notice is that with all the green plants in my tank the color seems to look green. To get a really good reading I have to put a piece of white plastic behind it to actually see the color.


 Thats one positive thing about the cheap little read sea unit. The cone in the center that is actually inside of it.... Is white.... making it pretty easy to see what color it really is.... for 8 bucks i am pretty pleased with my cheapo verson  haha... now is it were something that I was planning to keep in my tank all the time I would go for the more sexy glass work  however for just playing around with it to get a feel for if it works well.... and setting up CO2 flow after getting a tank refilled... it is serving its purpos well for me....

I to am running mine with a KH inside the "bell" of 5 degress.... seems like thats where people using these are leaning..... are you guys seeing proper CO2 levels going this route? good growth, little algae, BBA not appearing nor green spot? I know my fish seem to be just fine with it.... however I cant really comment about algae or plant growth.... its been... well never since I had anything good in that area  lol


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## hoppycalif

I notice a very few little spots of BBA on my heater, and on one plant leaf, so even with about 30-40 ppm of CO2, BBA can still grow. The plants are doing very well though, good strong color and consistent growth.


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## turbowagon

I got my Ebay version in the mail today.

My coworkers thought it was a crack pipe.


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## kamel_007

hoppycalif said:


> This works because a sealed container of air in contact with water will reach an equillibrium amount of CO2 that is at least proportional to the ppm of CO2 in the water. So, two containers with their water in contact with the same sealed container of air will reach the same ppm of CO2. The "drop checker" has distilled or DI water in it, with a known KH obtained with bicarbonate only - no other source of alkalinity, and no source of acidity. That makes the equation that is behind the pH/KH/CO2 table work correctly (see Chuck Gadd's website). So, if we can measure the pH of that little bit of water in the "drop checker", and we can, by using a pH indicator solution, we can accurately calculate how much CO2 is in that container of water, which will be the same as is in the tank water, since they are connected with a sealed air column. At KH=4, and 30 ppm of CO2, the pH will be 6.6 which turns the bromothymol blue indicator, used in almost all pH kits, green. So, green means you have the right amount of CO2 in the water, and yellow green means you have too much, while blue green means you have too little.
> 
> There is no way for the indicator solution to migrate to the tank water, since there is an air gap separating it from the tank water. If it did get into the tank water, it would be about 4-8 drops of a 4% sodium hydroxide in water solution with a little bit of bromothymol blue dye in it. It wouldn't be desirable to have it mixed into the tank, but I doubt it harming anything if it were mixed in.
> 
> So, to use this:
> First, get some distilled water from the grocery store.
> Using clean glass container, pour about a cup of that water into the container.
> Next, add a very small amount of bicarbonate of soda - baking soda - Arm and Hammer soda, etc. to the water and stir it up with a very clean stirrer.
> Test the KH of that water with your test kit.
> Most likely it will be a higher than 4 KH. So, add some more distilled water and repeat the test. (If the first KH comes out to 8 degrees KH, double the amount of water. If it is 6 degrees of KH, add 50% more water, etc.)
> When you get close to 4 degrees KH, repeat the test using twice as big a water sample in the vial as the kit calls for, then count each drop of KH reagent as being half the degrees of KH that the kit normally says - for AP test kit, that makes each drop equal to .5 degrees KH. I found I can get very near "exactly" 4 degrees KH by doing this carefully.
> Use a syringe to squirt some of this 4 degrees KH water into the bulb of the "drop checker". Fill the bulb about 2/3 full of the water.
> Add a few drops of your pH test reagent - use enough to get a strong blue color, but not so much that the water becomes opaque with the blue dye.
> Use the suction cup on the "drop checker" to suspend the device two or three inches below the tank water surface, with the "horn" of the "drop checker" pointing down so it traps air in the horn.
> 
> After a couple of hours or so the color of the "drop checker" fluid will be at about the equillibrium color, and that should be green if you have 30 ppm of CO2 in the water. If the color is yellow, you have at least 70 ppm of CO2 (and your fish are in serious trouble!). If it is blue, you have about 10 ppm of CO2, which is not nearly enough.


is the color will be the same of PH test color??

and the water inside the DROP CHECKER with KH of 4.. i do add 7 drops of PH test.. and do i've to add KH test drops?


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## elaphe

You need to look at one of the pH/KH CO2 charts and figure out where you want your CO2 levels. At a KH of 4, and a pH at 6.6, you have 30ppm of CO2. At a KH of 5 (what I'm running) you have a CO2 of around 38 to 40ppm. The pH regent will be green at a pH of around 6.6.

You need to use pure water (RO/DI, distilled, etc) and add enough baking soda to get your water to whatever KH you want (this is the fun part - trust me, it doesn't take much baking soda). You then put this water in the drop checker and add a few drops of pH test regent. You want it dark, but not so dark that you can't see through it.

It will be BLUE when you first put it all together. After about 2 hours, you will see that it has changed. If green, your good. Yellow, to much CO2; still blue, not enough CO2.

I noticed in my ADA catalog, they say to use your aquarium water. This won't give you an accurate measurement because of other contaminates in the water. I guess it would give you some kind of idea?

Brian op2:


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## hoppycalif

kamel_007 said:


> is the color will be the same of PH test color??
> 
> and the water inside the DROP CHECKER with KH of 4.. i do add 7 drops of PH test.. and do i've to add KH test drops?


The color will be the same as for the pH test kit, since that is what you are doing - measuring the pH of the bit of water in the bulb. It works because that water is "perfect" water for using the pH/KH/CO2 chart, unlike the tank water, which is far from "perfect". Don't add any KH test reagent to the bulb.


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## kamel_007

hoppycalif said:


> The color will be the same as for the pH test kit, since that is what you are doing - measuring the pH of the bit of water in the bulb. It works because that water is "perfect" water for using the pH/KH/CO2 chart, unlike the tank water, which is far from "perfect". Don't add any KH test reagent to the bulb.


OK.. im understand

SO i put 5 ml of water with KH of 4 and 7 drops of PH test.. as written in my PH test kit,

then.. i can't get this glass of drop checker.. it's not available in my country..

and till now.. i didn't find anything mach it.

could you help me?


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## hoppycalif

kamel_007 said:


> OK.. im understand
> 
> SO i put 5 ml of water with KH of 4 and 7 drops of PH test.. as written in my PH test kit,
> 
> then.. i can't get this glass of drop checker.. it's not available in my country..
> 
> and till now.. i didn't find anything mach it.
> 
> could you help me?


Page 1 of this thread shows one way to DIY one. Another way is to use clear plastic tubing, about a half inch in diameter. Bend a small "U" shape. Cement a plug in one end of the "U". Attach a suction cup to the side of the "U".

Another way to DIY one: Get a piece of one inch diameter clear plastic tube, about two inches long. Cement a disk of clear plastic on one end to seal it. Make another same size disk of clear plastic, except with a half inch diameter hole in the middle. Cement that on the other end. Get a piece of half inch diameter clear plastic tube, about one inch long. Cement it in the hole, with all of the tube sticking up into the big tube. All joints have to be water tight. Attach a suction cup to the side. Put the 4 dKH distilled water and reagent in the outside, big tube. Put it in the tank with the small tube opening facing down into the water.

I'm sure there are other ways to DIY one of these.


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## dennis

I used a propane torch to bend the test tube from a pH kit. It takes a little practice but the tubes are like $.50 so you can get a few extras. Teh trick is to spin it as you heat it and to make the bend, keep spinning it while pulling slightly apart and forming the bend.


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## epicfish

dennis said:


> I used a propane torch to bend the test tube from a pH kit. It takes a little practice but the tubes are like $.50 so you can get a few extras. Teh trick is to spin it as you heat it and to make the bend, keep spinning it while pulling slightly apart and forming the bend.


Oooh, I like this idea! =)


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## hoppycalif

I did some glass blowing in college, many years ago, but I still recall it being a lot of fun. You could actually make a usable version of this that looks almost like an ADA product, just by starting with that same test tube and heating the closed end until it shrinks a bit, then blow a bubble - not too big - heat the neck and bend it, then anneal the whole thing by heating all of it and letting it slowly cool. You could then heat the open end and use a carbon rod to open it to a larger diameter. Of course you could burn yourself, the garage, the house in the process, but it would still be fun for awhile!


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## kamel_007

hoppycalif said:


> I did some glass blowing in college, many years ago, but I still recall it being a lot of fun. You could actually make a usable version of this that looks almost like an ADA product, just by starting with that same test tube and heating the closed end until it shrinks a bit, then blow a bubble - not too big - heat the neck and bend it, then anneal the whole thing by heating all of it and letting it slowly cool. You could then heat the open end and use a carbon rod to open it to a larger diameter. Of course you could burn yourself, the garage, the house in the process, but it would still be fun for awhile!


Hmmm.. that's way to dangerous!!!


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## hoppycalif

Two questions people, including me, always ask are: How do you know the ppm of CO2 will be the same in the drop checker bubble and the tank water? And, how long does it take for the ppm of CO2 in the drop checker to match that in the tank water? I did some testing today to see if I could answer those questions.

I took a 2 cup measuring cup, mixed distilled water and baking soda to get about a 2dKH batch of water. Then I loaded the drop checker bubble with that water - it took 2 ml to do so. I added 4 drops of pH test reagent to the bubble. Then I installed the drop checker in the 2 cup measuring cup, with it just below the water surface. I took a length of air hose and used it to blow bubbles into the water to build up the ppm of CO2 in the measuring cup. About a minute of blowing got it to a pH of 6.5. I kept checking the pH until it rose to 6.6, which took about 30 minutes, then blew more bubbles for a minute and repeated that every 30 minutes. At various times I recorded what the pH of the drop checker water was, using the pH color chart. And, I charted the results:










You can see that the ppm of CO2 in the drop checker does equal that in the tank water, as closely as you can read the color of the test kit. And, it takes about 3 hours to reach equilibrium with the tank water. I wish it were faster in response, but 3 hours is certainly usable.


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## graedog

*Thanks*

Just a quick thank you

I found this post really interesting and helpful

Graeme


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## swifty1

Great post! - I've ordered 2 drop checkers, one amano style, one pear shaped, but one question - should the KH in the bubble be the same as the KH of the tank water?

or should it be worked out to give a green colour with the ppm level I'm seeking?

I think its the latter?


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## hoppycalif

The KH of the water in the bubble can be whatever you want to set it at. If you pick a KH of 4dKH, the bubble is green at 30 ppm of CO2. If you pick 5 dKH, the bubble is green at about 40 ppm of CO2. And, green is the most unambiguous color you can look for in the bubble, so it is best to chose the KH that goes with green at the ppm of CO2 you want to maintain. I am using 5 dKH for mine, and I'm having no problems with the fish at all. I am very tempted to try 6 dKH in the bubble, to get 45 ppm of CO2, but I haven't done so yet.

Another reason to use the KH that corresponds to green at the ppm of CO2 you want is that you then can detect ppm's that are much higher (yellow) or much lower (blue). If you used a KH where the color was yellow at the desired ppm of CO2 you couldn't tell the difference if the ppm were much higher. By that I mean, it is best to have the desired ppm give a color that is in the middle of the scale, not at one end of the scale.


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## swifty1

That's nice and clear Hoppy - thanks! 

Just waiting for my drop-checkers now!


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## hoppycalif

Another way to make a DIY drop checker is to use a small clear plastic bottle. Cut off the open end of the bottle, turn it over and glue it back in place upside down, so the neck extends into the rest of the bottle. Then attach a suction cup. Does anyone know what to use to glue P.E.T. plastic? It is a form of polyethylene so no glue I have found will stick well to it. I made a prototype this way using a bottled water bottle, but the joint didn't hold up at all. It works nicely though, but those bottles are really too big. I bought a 2.5 oz bottle of aloe and tried to use it but I heated it too much with hot water to clean it and the bottle suddenly shrank to a twisted mess! If that had worked it would be a $2 cost to make one.


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## dennis

You're best bet for sealing that is to use heat and fuse the two parts together. Make sure the two peices are equal by careful trimming and/or sanding with the two halves jammed together. Then, heat a piece of metal on the stove or with a torch until you can just barely melt the plastic with it. I don't think there is any glue that wil stick to it for more than a few days.


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## hoppycalif

dennis said:


> You're best bet for sealing that is to use heat and fuse the two parts together. Make sure the two peices are equal by careful trimming and/or sanding with the two halves jammed together. Then, heat a piece of metal on the stove or with a torch until you can just barely melt the plastic with it. I don't think there is any glue that wil stick to it for more than a few days.


Thank you Dennis. I will try that next. My grocery store had some little 2.5 ounce bottles of a hand cleaner too, but the bin was empty. That should work better than the aloe bottle, and it's $2 too. Hey, big spender!!


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## hoppycalif

*Diy*

I dug down deep and bought another 2.5 oz bottle of aloe to try to make a drop checker. These pictures show my progress:

First, the bottle still filled with goo, with the razor cut across the top:









After making another cut to get rid of the excess height:









After using sissors to trim the pieces:









The pieces ready to assemble:









After "welding" the bottle parts together, and attaching the suction cup, plus adding a bead of silicone to make it leak tight: (as it sits here, it is upside down - the opening will be on the bottom in the water.)









Welding isn't easy. I used a knife blade heated with a torch, using the scrap part of the bottle to judge when it was hot enough. Then I gently rubbed the joint with the hot blade to melt it together. Unfortunately, that left a couple of slight gaps which could not be sealed by any further welding. So, I used some aquarium silicone sealant to seal the entire joint.

The suction cup is installed in a hole that is melted into the side using a drill bit heated by the torch. I started small and kept going larger until the suction cup could be forced into the hole. That is a bit tricky too.

Now, you, along with me, are going to have to wait for the silicone to dry to see if this will work. (My faithful assistant, Igor, is circulating now accepting bets!)


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## dennis

The weak part to this may be the hole for the suction cup. Hopefully though, the rubber will swell slightly when wet and prevent any leakage. The silicone may not stick very well but if it is only for small holes it will probably be OK. In hindsight, a way or heat crimping the joint may be best, similar to the way they seal those damn packages for portable electronics. Heated pliers may do the trick.....


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## kamel_007

hoppycalif said:


> I dug down deep and bought another 2.5 oz bottle of aloe to try to make a drop checker. These pictures show my progress:
> 
> First, the bottle still filled with goo, with the razor cut across the top:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> After making another cut to get rid of the excess height:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> After using sissors to trim the pieces:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> The pieces ready to assemble:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> After "welding" the bottle parts together, and attaching the suction cup, plus adding a bead of silicone to make it leak tight: (as it sits here, it is upside down - the opening will be on the bottom in the water.)
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Welding isn't easy. I used a knife blade heated with a torch, using the scrap part of the bottle to judge when it was hot enough. Then I gently rubbed the joint with the hot blade to melt it together. Unfortunately, that left a couple of slight gaps which could not be sealed by any further welding. So, I used some aquarium silicone sealant to seal the entire joint.
> 
> The suction cup is installed in a hole that is melted into the side using a drill bit heated by the torch. I started small and kept going larger until the suction cup could be forced into the hole. That is a bit tricky too.
> 
> Now, you, along with me, are going to have to wait for the silicone to dry to see if this will work. (My faithful assistant, Igor, is circulating now accepting bets!)


Looking forward to see i t working!


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## hoppycalif

OK, it works! It isn't beautiful, but it works and it is dirt cheap. I had to use a bit of silicone sealant to seal the hole where the suction cup mounts, but once that cured for a couple of hours it has been water and air tight. It took about 2 1/2 hours to reach the same green color as my ADA style drop checker. Here they both are, in the tank - still green with GDA for another day.


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## Fome

I've an odd request.


I do not have a KH test kit. Is there any way you could "estimate" how much baking soda it would take to reach KH of 4.0 in a certain volume of DI water? ie. a cup, 100 ml, etc.

As I understand, it's not extremely important to get exact values on co2, just estimates on if your plants are getting enough and your fish aren't in imminent danger.

I plan on making one of these soon!
I already have sealant, suction cup, ph indicator fluid, and an adequate bottle.
Except for the DI water, this'll be one of the few parts of my tank that cost me nearly nothing!

Appreciated!


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## kamel_007

hoppycalif said:


> OK, it works! It isn't beautiful, but it works and it is dirt cheap. I had to use a bit of silicone sealant to seal the hole where the suction cup mounts, but once that cured for a couple of hours it has been water and air tight. It took about 2 1/2 hours to reach the same green color as my ADA style drop checker. Here they both are, in the tank - still green with GDA for another day.


Your tank glass look's like green!

DO you've an algea bloom?


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## hoppycalif

Yes, I have GDA in the last throes of its life cycle. If all goes according to plan I will be wiping it off today.

Fome, KH test kits are very cheap and very useful, unlike many other test kits. Aquarium Water Testing: Aquarium Pharmaceuticals GH/KH Test Kit I don't know any reliable method for making water with a specific KH other than testing and retesting, and even that can be difficult.


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## dennis

If I have done the math correctly, trust me, I probably did not....

Using NaH2CO3 to get 5degrees requires 75.18mg in 1 liter of RO/DI water.

For comparison, a penny weights 2.6 grams or 2600mg.

Anway, if you buy a 1 gallon jug of RO/DI (3.79liter/gallon) you need to add 284.9mg or .285g NaH2CO3. The only way to accurately measure this is to use a gram scale.


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## bpimm

Another way to weld the plastic bottle is to use a cheap soldering iron, the lower the wattage the better. Then you can use the extra bottle material cut in strips for welding rod to fill in the gaps.

I have used a variac to control the heat of the soldering iron. you may be able to use a dimmer to turn it down a bit also.


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## hoppycalif

bpimm said:


> Another way to weld the plastic bottle is to use a cheap soldering iron, the lower the wattage the better. Then you can use the extra bottle material cut in strips for welding rod to fill in the gaps.
> 
> I have used a variac to control the heat of the soldering iron. you may be able to use a dimmer to turn it down a bit also.


When I moved last year and got rid of my workshop tools I apparently also got rid of my soldering gun and iron. In any case I couldn't find them. I suspect that they would be much too hot for PET plastic - there seems to be a narrow temperature band when the stuff welds and doesn't char. Don't even the cheap soldering irons have a temperature control of some kind built in? If so, how would dropping the voltage affect the temperature?

The DIY drop checker was still working this morning, with no leaks that I can detect. It finally worked loose from the glass, probably due to the GDA on the glass, and began floating around the tank. So, I removed it at noon - I consider it to be a success!


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## bpimm

hoppycalif said:


> When I moved last year and got rid of my workshop tools I apparently also got rid of my soldering gun and iron. In any case I couldn't find them. I suspect that they would be much too hot for PET plastic - there seems to be a narrow temperature band when the stuff welds and doesn't char. Don't even the cheap soldering irons have a temperature control of some kind built in? If so, how would dropping the voltage affect the temperature?


The cheap ones are not thermally controlled, That's why I used the Variac to control the temp. a variac is a variable transformer so it just lowers the voltage. a soldering iron is a resistive load just like a light bulb, so a standard dimmer may work to do the job as long as the wattage of the soldering iron is within the rated wattage of the dimmer.


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## dennis

Here is my contribution to the DIY drop checker:

Took me about 15 m inutes and a Benzomatic torch. Truth be told though, I have been dinking around with this for a few days and this is my 5th attempt. Not great but functional and fun to do. I never considered heating and actually blowing the end until hoppy suggested it. Also, you'll notice the end is broken, apparently a screw driver is not a substitute for a carbon rod to flare the end. After it broke I did heat the end so it is not sharp and the fishies are safe. This may turn out ok though as it broke at a real angle meaning that the water interface is a little larger than it would be otherwise. kH is 4.2 (Lamotte-80ppm) and solution has about 4 drops of indicator from the AP pH test kit.


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## hoppycalif

Hey, that looks neat Dennis! I still lack the nerve to try to blow glass. It is one thing to do that in a well equipped lab, with the right equipment, but in my garage, with flammable stuff everywhere? Now, if I could blow one with wood I would be going at it. 

Rethinking my experience as a college student glass blower (in 1959), the way to do this correctly is:
1. start with a piece of 3/8 inch diameter glass tubing.
2. heat one end red hot. 
3. gently blow in the other end while turning the tube around its axis so it doesn't droop.
4. Stop when you have the desired ball diameter.
5. Anneal it by gently heating the whole end area and letting it slowly cool.
6. heat an area about 2 inches away from the ball until red hot.
7. gently blow until that part flares out into another ball.
8. Anneal it again.
9. heat between the two balls until red hot
10. gently blow - very gently - while bending the tube about 135 degrees angle. The blowing is to keep the tube from collapsing.
11. Anneal the whole thing again.
12. The hard part: use a diamond point tool to scribe a cut arount the second ball, so when it snaps off there you have the desired flare left.
13. Heat the cut edge to round it
14. anneal the whole thing one last time.

And, don't forget the very first rule - buy lots of glass tubing so the tenth try will finally all work out well!


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## dennis

Ahh, good explination. The hardest part with mine was making the angle without it collapsing. I thought you were supposed to pull and bend but blowing and bending sounds like it would work better. unfortunately, all this is hard to do with a 3" long test tube. Blowing the ball end was really cool and I have never done anything like that before.

I may need to go find some glass tube locally...

Anyway, back to the subject at hand


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## schaadrak

Try using a heat gun (like a hair dryer, but hotter) to weld PET plastic. That way if it gets too hot you can just back off a little.

Also maybe try using two different bottles of different diameters. Use the bottom off of the smaller one and flare it out where it meets the top of the larger. That way you get more surface to surface contact which means a stronger weld.


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## Blacksunshine

dennis said:


> Here is my contribution to the DIY drop checker:
> 
> Took me about 15 m inutes and a Benzomatic torch. Truth be told though, I have been dinking around with this for a few days and this is my 5th attempt. Not great but functional and fun to do. I never considered heating and actually blowing the end until hoppy suggested it. Also, you'll notice the end is broken, apparently a screw driver is not a substitute for a carbon rod to flare the end. After it broke I did heat the end so it is not sharp and the fishies are safe. This may turn out ok though as it broke at a real angle meaning that the water interface is a little larger than it would be otherwise. kH is 4.2 (Lamotte-80ppm) and solution has about 4 drops of indicator from the AP pH test kit.


Thats brilliant. I think I will grab a test tube and give that a shot.


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## joetee

May I ask what a Drop checker is?

Never mind. I figured it out.


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## yoink

dennis said:


> Ahh, good explination. The hardest part with mine was making the angle without it collapsing. I thought you were supposed to pull and bend but blowing and bending sounds like it would work better. unfortunately, all this is hard to do with a 3" long test tube. Blowing the ball end was really cool and I have never done anything like that before.


This may sound silly but, how do you blow the glass without burning your mouth? It seems like a small test tube would heat up rather quickly.


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## hoppycalif

Glass is a good insulator, so you can have one end of a glass tube at glass melting temperature - red hot - while 6 inches away or less, the glass isn't even warm. That's why you can blow glass safely - just never suck instead of blowing. And, you don't really blow, like you would blow a balloon, you just move some air in to reshape the molten glass. It is extremely easy to blow a hole in the end if you blow hard at all. Another secret is that if you just closed the end of the tube by melting it, then tried to blow a bubble there the glass would get very thin and break. So, you need to first thicken the end a bit by.....as I recall they use a carbon block to rub the end to push it back to thicken the glass. If you do this in the middle of a tube you just push the end of the tube back towards your mouth and that thickens the glass a bit. It is fun and it is easy to just blow a simple ball, but very tricky to get much more complicated.


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## swifty1

Just received my 2 drop checkers from HK today - one tear drop shape and one amano style Type 1. Good delivery, 7 days from ordering.

They both look good although no instructions what to do (well, it says fill up to the water line with tank water on the reagent bottle but this is for normal Co2 testing in a test tube, not for this drop checker, and there's no 'line' on the DC's) - thank god for this post! 

So, off to get some distilled water on way home from work and will let you know how I get on!


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## Blacksunshine

yoink said:


> This may sound silly but, how do you blow the glass without burning your mouth? It seems like a small test tube would heat up rather quickly.


I found it a good idea to use the tube from a bic pin and tape it into the open end of a test tube. this makes it easier to roll the tube around while you heat it evenly so you don't have a blow out on one side or unevenly formed bubble. Slow air pressure pressure is important when blowing so you don't expand the glass too quickly. I also use a propane torch for this so it heats it quickly. Just besure that the room you are doing it in is not too cold or the tube will crack from cooling too quickly.


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## kamel_007

hii.. 

i just made my DIY drop checker.. with KH of 5.

but the solution is still blue!! after 5 hours and blue?

why??


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## yoink

I just made one from a glass test tube. It doesn't look half as good as denis' though. I couldn't get the glass to bubble out at the end, just slightly rounded. Function over form I guess. Testing to see if it works now.


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## hoppycalif

The only good reason to have the bulb is so it holds enough distilled water/indicator solution so you can easily tell what color it is. Otherwise it functions with or without it.


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## dennis

yoink said:


> I just made one from a glass test tube. It doesn't look half as good as denis' though. I couldn't get the glass to bubble out at the end, just slightly rounded. Function over form I guess. Testing to see if it works now.


The trick for that seems to be hotter than you think and to put the tip of the flame directly on the corned of the tube where the 90 degree angle is.


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## MrSanders

> hii..
> 
> i just made my DIY drop checker.. with KH of 5.
> 
> but the solution is still blue!! after 5 hours and blue?
> 
> why??


Seems to me like its still blue beacause its doing its job.... That is, if it's made correctly and allowing for the two solutions to reach eq with each other. It would indicate that you dont have enough CO2 dissloved in your tank. *hint* the whole point of having a drop checker  to be able to moniter a general estimated amount of CO2 in the water..... if its blue not enough... green means good to go, yellow.... well Im still playing with that one, for me yellow doesnt always mean to much CO2.... but in general your fish are going to let you know about when there is too much


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## hoppycalif

MrSanders said:


> Seems to me like its still blue beacause its doing its job.... That is, if it's made correctly and allowing for the two solutions to reach eq with each other. It would indicate that you dont have enough CO2 dissloved in your tank. *hint* the whole point of having a drop checker  to be able to moniter a general estimated amount of CO2 in the water..... if its blue not enough... green means good to go, yellow.... well Im still playing with that one, for me yellow doesnt always mean to much CO2.... but in general your fish are going to let you know about when there is too much


Those of us who were believing the pH/KH/CO2 chart and thought we had plenty, if not too much, CO2 in the water, can now tell if we really do have the 30-40 ppm we should have. And, most of us will have to crank up the bubble rate to get there - to get the blue to change to green. That is the advantage of this method - it truly is an accurate way to measure the ppm of CO2 in the tank water. The only errors will be our judgement of the color green, and our mistakes in setting the distilled water KH at 4 or 5 dKH. We can reduce the effect of those mistakes by being very careful in how we judge the color and the KH of the distilled water.

When the bulb is yellow, with 4dKH distilled water, that means a pH of about 6.0 to 6.2, or 75 to 120 ppm of CO2! That is too much! I doubt anyone believing that even 75 ppm is tolerable in the tank. Of course if the bulb is only slightly yellowish green, the ppm may still be ok.


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## kamel_007

hoppycalif said:


> Those of us who were believing the pH/KH/CO2 chart and thought we had plenty, if not too much, CO2 in the water, can now tell if we really do have the 30-40 ppm we should have. And, most of us will have to crank up the bubble rate to get there - to get the blue to change to green. That is the advantage of this method - it truly is an accurate way to measure the ppm of CO2 in the tank water. The only errors will be our judgement of the color green, and our mistakes in setting the distilled water KH at 4 or 5 dKH. We can reduce the effect of those mistakes by being very careful in how we judge the color and the KH of the distilled water.
> 
> When the bulb is yellow, with 4dKH distilled water, that means a pH of about 6.0 to 6.2, or 75 to 120 ppm of CO2! That is too much! I doubt anyone believing that even 75 ppm is tolerable in the tank. Of course if the bulb is only slightly yellowish green, the ppm may still be ok.


I found out the reason.

i've an external filter that built in with the tank hood, and it's type wet dry that came with spray bar..

i stopped the filter for about 4 hours and notice the color of my drop checker is turned to slight green..

with KH of 5 and look's like PH of 6.5 means i've enough CO2,,

even the plant's it's pearling like it never was!!...

then.. now i know the "Drop-Checker" give's the accurate amount of Co2 in my tank..

when testing the water with usually test kit.. test KH and PH and estimate how much CO2 you have.. that's not accurate... DON'T BELIEVE IT!!

Now by MR.Drop-Checker you'll be able to know how much of Co2 you have..

"LIKE YOU NEVER KNOW"


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## bpimm

The welded bottle drop checker got me thinking that there has to be a simple way to make a drop checker out of readily available materials that are cheap.

What I came up with I think is easy enough for anyone with a little of the DIY gene. Everything I used came from a LFS except the glue which came from a good hardware store (also available from Tap Plastics online).

The materials are as follows 
1 3/16" Lee undergravel filter lift tube
5/8" Lee undergravel filter lift tube
Top Fin airline tubing holders
Acrylic cement


















To make this project you need to have some flat plastic for the end caps. Preheat your oven to 200 Degrees F, cut off a piece of the larger tube that is longer than the tube is wide, 1 1/2" should be good. Then cut the tube lengthwise with scissors, Place this piece in the oven on a cookie sheet or any other surface to keep it from falling through the rack. heat until pliable, remove from heat and flatten the plastic by hand and let cool. Gloves can help at this stage, I just lay it out on the counter top and hold it down until it cools. Now you need two flat pieces to stack with the plastic between them for the final flattening. I used two lids off of some glass jar canisters. Place the plastic piece on one surface and lay the other on top, I added a cup of water for weight, bring it up too temperature, leave it hot for a few minutes, then let cool.

























nice flat piece of plastic to work with.

Now cut a piece of the larger tube for the body of the drop checker, I made mine 1 1/4" long, I used a chop saw to cut it but any saw or even a knife can cut this material. The Chop saw gave me nice true ends to work with which is important for a good glue job, if you use a less true way to cut the tube then you can true up the ends by laying sandpaper on a flat surface and rubbing the tube end on the sandpaper. Once the ends are true glue the tube down to a piece of the flat material. I then ran a bead of glue around the inside to insure a good joint.

Sorry about the focus on this one.








I sat a weight on top and let sit until the glue cured.

Next take one of the clips for the airline holders.









and trim off the actual clip to give you a flat surface to glue to.









and glue to the side of the body.

















Now you need to make the bottom end, to do this you need a hole in the flat material the size of the smaller tube, to cut this hole I used a step drill.









These bits are a very useful tool as they will drill a true round hole in thin material. If you don't have a step drill cut the hole with a hobby knife and sand to fit. Cut a piece of the smaller tube 1/2" shorter than you cut the body and glue it into the hole flush with the end, let dry.
Now take the two pieces and glue together lining up the smaller tube in the center of the larger one and let dry.

















This is the bottom









Trim the excess material off of the ends using scissors then file or sand the joints smooth. I hit it with a buffing wheel to clean it up but it's not necessary.

Stick the suction cup on and you are ready.

















Happy building
Brian


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## epicfish

Hm, wow, looks great. =) Time to head out to the LFS and get me some lift tubes. =)


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## dennis

That's very clever. Well done. A suggestion though, next time try painting the inner tube white so that the color of the indicator is easier to see.


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## hoppycalif

Wow! That is a neat way to make one of these. How much did the materials cost you? I wonder if a TAP plastic store would sell such small lengths of tubing? I know you can buy a foot of most of their tubing sizes, but I don't think you can an inch. Acrylic is a great plastic to work with since it is so easy to glue.


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## hoppycalif

dennis said:


> That's very clever. Well done. A suggestion though, next time try painting the inner tube white so that the color of the indicator is easier to see.


TAP plastics sells white acrylic tubing I think. If so, that would work best of all.


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## bpimm

A white center tube would help.

My total cost was $1.99 for the suction cups, I already had the rest. I saw at pet smart some lift tubes for $2.99. I had paid under $5.00 for the 3' lengths.

If you went out to but everything from scratch it would be about $15.00 but that's enough to make 10-15 of these guys. so the actual cost is around $2.00 EA. It would be a great project for a club to get together and make a bunch.


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## gpimm

Another source for white center tubes would be the standard white PVC pipe. Not sure if the acrylic glue will work but you could use the "Multi-porpose cement" for plumbing fittings. It glues PVC, CPVC, and ABS. I use this to glue 1/2" CPVC pipe caps on the 5/8" clear aquarium tubing to make bubble conters.

Gary


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## Blacksunshine

gpimm said:


> Another source for white center tubes would be the standard white PVC pipe. Not sure if the acrylic glue will work but you could use the "Multi-porpose cement" for plumbing fittings. It glues PVC, CPVC, and ABS. I use this to glue 1/2" CPVC pipe caps on the 5/8" clear aquarium tubing to make bubble conters.
> 
> Gary


Acrylic glue will work fine with PVC. Or you can use the pipe glue.

And that is a GREAT idea!. I will be making a couple tonight.
Luckly I have a TAP plas's around the corner from my house.


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## hoppycalif

My wife occasionally has artificial finger nails "installed", and they are built up using acrylic plastic. She uses ordinary nail polish on them, so if you use white nail polish (is there such a thing???) it would work fine on the acrylic pipe.


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## kamel_007

This's My Diy "drop-checker"


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## hoppycalif

kamel_007 said:


> This's My Diy "drop-checker"


Is that a shot glass? How did you make it? Once you understand how simple this device is, there must be a dozen ways to make one. The absolute simplest I have heard yet is to take a plastic tube, bend it into a "U" shape and cap one end. Of course a suction cup is still needed, but there are lots of options for that too.


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## dennis

*Time to kick it up a notch!*

OK, while I am discovering that I really like to melt glass (maybe a new hobby for me. I can be a double threat!) I just don't like the uncertaintly of this. The whole yellowish, greenish thing is just to much for me.

So, I give you the electronic drop checker:


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## hoppycalif

dennis said:


> OK, while I am discovering that I really like to melt glass (maybe a new hobby for me. I can be a double threat!) I just don't like the uncertaintly of this. The whole yellowish, greenish thing is just to much for me.
> 
> So, I give you the electronic drop checker:


Dennis, how did you seal around the probe, to keep the air from leaving the drop checker? Incidentally, you beat Tom Barr to this! He has been posting about making one of these by mid December. The only non-fool-proof part of this design that I see is the electrical interferrence issue. How do you satisfy yourself that the probe is not being affected by interferrence?


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## dennis

Re: the seal.

I started playing around with tubing and discovered thet my PinPoint probe was a good fit for 1/2" eheim tubing. Next, I played around and found a 5/8" forstner bit that was a good fit for the slightly expanded tubing around the probe. I pushed a short piece of tubing onto the probe, easiest when wet, and then forced (gently) the tubing/probe into the hole in top of the "checker". No leaks. I also know the tubing will expand a tiny amount when underwater for a while, which should improve the fit even more. YMMV with regards to probe size, tubing availibility and drill bit size. I probably got lucky that I had a bit that fit well.

An alternate method would be to use a specially made connector that holds the probe. I know IUnknown made an inline probe holder using one of these fittings.

Now, re: electrical interferrence, I have wondered about that several times in the past. Each time I double checked the reading with everything on verses everything off and unplugged. Never any issues.

Now, I have been using the regular drop checker for several days and find that with kH ~5 the indicator is yellow by the end of the day. The fish are fine, maybe a little skittish but fine. I have not adjusted the CO2 flow at all. My electronic drop checker (we need a name for this) has stabilized at 6.3 after 3.5 hours. The water to air interface is much larger on this than on the little drop checkers so I am pretty confident that everything is about right. The water in the electric version is probably not as alkaline as in the drop checker. My next step, now that it works, is to get some DI and make a proper solution of kH 5 and set the controller to ph 6.5, which will give me ~45ppm CO2.


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## hoppycalif

I wait with bated breath to see what the effect of 45 ppm of CO2 is on the fish and shrimp. (No, seriously, I plan to take a breath now and then.) When I first set up my ebay dropchecker the color went to yellow pretty quickly, with 4dKH water in it. And, all of the fish were gasping at the surface. So, I think there is a narrowing range of higher ppm's available to check out. Once I get my GDA problem solved for good, and my aquascape fixed - too much hygrophila now - I will switch to 6 dKH water in mine, to see if 45 ppm works for me.


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## dennis

I finally got some distilled water and made up some kH 5 water. Here is what I found to be easiest: 6grams NaHCO3 raises 50 liter of water ~4 degrees. I can acurately measure 500ml so 4degrees in 500ml is .06gram. Now, my gram scale has a readout of .1gram so to get a nice round number, .06*5=.3g. So, add .3 gram to 50ml of water. That way, 10ml of that solution (suck it up with a syringe) in 490ml water is about 4 degrees. Test with Lamotte reads 4.04 degrees. So, add 2ml more and test again. kH=5 degrees.


I have a confusing issue now though. I mixed a small dropper bottle of this solution with 2drops per ml of indicator and filled my little drop checker. I also used the same 5kH mix w/o indicator to fill my electronic drop checker. I had calibrated the probe yesterday but the electronic checker settled overnight at a reading of 6.1. The color checker is blue green. There is definitely a big descripency but I can't think of what the problem may be. My initial thought is that the probe end, which absorbs water is effecting the readout.

Maybe I should soak my probe in distilled for a while to try and pull any kH in the probe out by osmosis. Also, I am wondering if I should use a lower kH in the electronic version since it may make the gas transfer happen faster- lower kH means biggger pH swings. I am thinking I should buffer to .5-1 degree for that.

Any thoughts?


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## hoppycalif

I have been thinking about the electronic version - the "requirements" for the solution in it are much different from that of the indicator solution version. The latter needs water with a KH of 4-5 dKH so that the color will be green at the CO2 ppm that is desired. But, the electronic one doesn't have that need, so for that one it is best to set the KH to where the pH will be about 7 at the desired ppm of CO2, and that is at about 13 dKH. (Because most pH probes are calibrated to be right on target at 7.01 pH.) I don't understand how a pH probe works well enough to be able to figure out why your reading seems to be off. My pH probe has always been so erratic that I don't trust it at all, and it is too bulky to be used for a drop checker anyway. I just wasted my money when I bought it.


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## dennis

I'm not sure about that. A kH of 13 woudl mean you inject lots of CO2 before getting a pH change. That means you would OD you tank on CO2. I think better would be to use a very low kH so that the pH change happens fast and easily, allowing the controller to be more in control. I do not think it matters if the probe reading is at 7 or at 5, it will still be as accurate as the probes accuracy. What I mean is, I do not think that having a lower pH as the setpoint will compound any probe inaccuracies. Therefore, a lower kH will mean a faster response time... I think.


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## hoppycalif

dennis said:


> I'm not sure about that. A kH of 13 woudl mean you inject lots of CO2 before getting a pH change. That means you would OD you tank on CO2. I think better would be to use a very low kH so that the pH change happens fast and easily, allowing the controller to be more in control. I do not think it matters if the probe reading is at 7 or at 5, it will still be as accurate as the probes accuracy. What I mean is, I do not think that having a lower pH as the setpoint will compound any probe inaccuracies. Therefore, a lower kH will mean a faster response time... I think.


With a 13 dKH water reference you get:
pH - 6.6 = 100 ppm CO2
6.7 = 80
6.8 = 60
6.9 = 50
7.0 = 40
7.1 = 30
7.2 = 25
7.3 = 20
7.4 = 15
7.5 = 10

The amount of CO2 introduced into the tank wouldn't be affected by the KH of the drop checker water, nor would the amount of CO2 to be absorbed by the drop checker be affected. The goal should be to make the KH be such that around the ppm of CO2 you want, the changes in pH per change in ppm of CO2 are a maximum. At a KH of 1dKH you get:

pH - 5.5 = 95 ppm CO2
5.6 = 75
5.7 = 60
5.8 = 50
5.9 = 40
6.0 = 30
6.1 = 25
6.2 = 20
6.3 = 15
6.4 = 10

So, I conclude that the only effect of KH is to shift the pH range that is of interest, and it seems to me that the closer that is to 7.01, where you do a one point calibration, the more accurate the pH probe/meter is. (All of the above ppm values are rounded off to the nearest 5 ppm)

I also manipulated the equation for ppm vs KH and pH to find at what KH the change in pH vs ppm is a maximum - and, as the tables above show, the change in pH vs ppm is not dependent upon KH.


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## wiste

How long do you leave the drop checker in the tank? I understand there is a minimum time that you have to leave it in the tank but I am curious to know if you leave it in the tank over a long period, days or even weeks and use it like a thermometer.


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## epicfish

wiste said:


> How long do you leave the drop checker in the tank? I understand there is a minimum time that you have to leave it in the tank but I am curious to know if you leave it in the tank over a long period, days or even weeks and use it like a thermometer.


Yes, it's held in there with a suction cup indefinately so that you can always glance over at it and know approximately what your CO2 levels are.


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## hoppycalif

Yesterday I learned that Dennerle makes this device, complete with reference solution with indicator reagent in it. They call it "CO2 Long Term Test Correct" and it is made of plastic. The reference solution (distilled water with bicarbonate in it?) has a KH of about 3dKH, to give a green indication at 20-25ppm of CO2 in the water. The configuration looks to be about that of the teardrop shaped glass one that is sold on ebay. So far I haven't seen this device for sale in the US, but it is in the UK and Europe.

Based on Dennerle's instructions, the solution in the device needs to be replaced about once a month because the indicator, which is a dye, will fade with exposure to light over that period of time.

I suppose in a few weeks someone will point out that Leonardo da Vinci first invented this device back a few years ago!


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## wiste

> So far I haven't seen this device for sale in the US


Try a web search for 'Dennerle CO2 Visual Indicator'. If this is the same product it is available.


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## hoppycalif

wiste said:


> Try a web search for 'Dennerle CO2 Visual Indicator'. If this is the same product it is available.


Yes, that is it! For some reason I couldn't find those suppliers when I googled it yesterday. $17 plus shipping - not too bad unless the shipping cost is exhorbitant.


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## hoppycalif

Here is a simple way to DIY this, using clear acrylic tube in 1 inch diameter and 1/2 inch diameter, plus two acrylic discs 7/8" in diameter and one such disc 3/8" in diameter. Tap Plastics has all of these shapes.










The advantages are:
The air gap has a maximum area and minimum length to decrease the response time.
The tube of indicator solution is small enough to take very little solution, but is easily viewed in the aquarium.
It can be mounted in the tank with a "heater holder" suction cup device made for a 1" diameter tube. The clip can be easily cemented to the device.
It is small enough not to be overly obtrusive in the tank.

But, the disadvantage is that it takes a syringe with a bent needle to squirt in the solution.

I haven't made this yet, but will do so shortly.


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## Laith

hhmmm... if one could add threads or a perhaps an o-ring to make a tight fit the top part of the unit could perhaps be removable?


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## fredyk

I was wondering if I could heat a test tube thing on the gas cooking range, fill it with sand or salt, and bend; or would the heat distribution be inadequate?
Mark


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## swifty1

I received my two types of drop checker from HK recently and have to say that I'm extermely pleased with both of them.

It was fiddly trying to get 4 dKh in distilled water, especially as i was running out of KH reagent but finally did it.

the drop checkers seem decent quality and both look good. My comments on them are that there are no instructions with them and the reagent is from a CO2 tester and doesn't mention using distilled water of known KH or anything - just 5 drops of the reagent into 'some' tank water. Oh. and why oh why do thye come with black suckers rather than clear ones? These are minor points and would not stop me buying any more.

Thank god for this post which inspired me to buy them in the first place. I give them a glance every morning and has taken all the guesswork out about Co2 levels - it's already saved a lot of tests and calcs - thanks Hoppy!


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## redstrat

Swifty do you notice any difference in the two styles as far as response time for a color change. Does one seem to lag behind the other?


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## turbowagon

My drop checker (kH approx 5) still reads green the next day before the CO2 comes on again, which I guess is a good thing, but it surprised me. I confirmed that when I remove the drop checker from the tank, after a few hours the color is a deep blue (approx 7.5-7.6 pH).

I expected that much of the CO2 would outgass overnight, but I guess I was wrong. I run my spraybar horizontally at one end of the tank, angled slightly downward, which produces a slight surface ripple.


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## hoppycalif

My drop checker fluid goes to blue green overnight, then back to green in a couple of hours with the CO2 on. I was a little surprised at how little of the CO2 is lost overnight too.

fredyk: I don't think a gas range will be enough heat, concentrated enough to allow you to bend a glass test tube. If you try it, don't put anything in the tube, like sand, or it will make it much harder to heat up the area hot enough, and it will tend to imbed into the glass. The way real glass blowers do it is to slowly push the ends of the tube to shorten the test tube, thickening the glass where it is to be bent, then very gently blow into the tube as you bend it. That is a lot easier with a longer tube, of course. If you try this, be very careful!!


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## jeff5614

Great thread. I ordered the ADA style knockoff yesterday and can't wait for it to arrive. Sometimes I think I enjoy the "stuff" as much as the fish and plants, lol.


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## bpimm

hoppycalif said:


> Here is a simple way to DIY this, using clear acrylic tube in 1 inch diameter and 1/2 inch diameter, plus two acrylic discs 7/8" in diameter and one such disc 3/8" in diameter. Tap Plastics has all of these shapes.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> The advantages are:
> The air gap has a maximum area and minimum length to decrease the response time.
> The tube of indicator solution is small enough to take very little solution, but is easily viewed in the aquarium.
> It can be mounted in the tank with a "heater holder" suction cup device made for a 1" diameter tube. The clip can be easily cemented to the device.
> It is small enough not to be overly obtrusive in the tank.
> 
> But, the disadvantage is that it takes a syringe with a bent needle to squirt in the solution.
> 
> I haven't made this yet, but will do so shortly.


From the looks of the design it could just float in the tank also, only problem I see is you would have to hunt for it to check it. 

I run my CO2 24/7 and the indicator solution stays the same color night and day. Maybe the plant uptake is a minor part of the total CO2 injected into the tank so the CO2 content of the tank water stays the same whether the plants are using it or not.


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## swifty1

Nah, i didn't really see any real difference in response times between the 2 styles. They both changed to green within 2-3 hrs, although you can see a colour change within about 30 mins.

I run my Co2 24/7 so don't notice any subtle colour change overnight.

When i first installed them the teardrop shaped one was almost yellow so I tuned down the Co2 a bit.

I've just bought a solenoid valve so may add this to the bigger tank overnight, pureley to save on Co2. If I notice any colour change overnight when I fit it I'll let you know.


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## redstrat

Thanks Swifty, I was just wondering if there is any efficiency difference between the two designs. It looks to me that one of them has more air space inside. It seems to me that a larger internal air space would slow down the color change time, but I'm sure surface area is a bigger factor. Surface area of the tank water interacting with the air in the drop checker and surface area of the indicator solution. I'm glad to hear that my suspicions are either false or this just is too small of a scale for it to really have an effect.


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## hoppycalif

davis.1841 said:


> Thanks Swifty, I was just wondering if there is any efficiency difference between the two designs. It looks to me that one of them has more air space inside. It seems to me that a larger internal air space would slow down the color change time, but I'm sure surface area is a bigger factor. Surface area of the tank water interacting with the air in the drop checker and surface area of the indicator solution. I'm glad to hear that my suspicions are either false or this just is too small of a scale for it to really have an effect.


Logically I would expect the fastest reaction from one with a large area of contact between the tank water and the air gap, and, because the amount of water in the bulb is so small, the area of contact between the bulb water and the air gap would be a secondary factor. I'm not sure, but I doubt that the length of the air gap would enter into it. But, a large air volume would seem to slow it down. I don't know anything about the equations that would govern the rate at which equilibrium is reached between a pocket of air in contact with water, so intuition is all I have to go on.


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## hoppycalif

Last week I took a trip to Tap Plastics, where I bought a 1" dia, 1/16" wall thickness acrylic tube, to go with my existing 5/8", 1/16" wall acrylic tube, and some acrylic disks - 1", 1/2", 5/8" diameter, plus a tube of medium viscosity acrylic cement. Then I spent a couple of hours yesterday and a couple of hours today, using only hand tools plus a cordless drill to make a couple of DIY drip checkers. The first one is probably the fastest reacting one:































The second one is probably the easiest to read the color on. I used white fingernail polish to paint the inside of the air gap tube which becomes the background for the fluid in the bulb.
























Tomorrow I plan to load both with distilled 5 dKH water and reagent and place them in the tank at the same time, to see how they compare. I will post those results, too.

Edit: Today I loaded them and added them to the tank.









Edit: After two hours all three of the devices have the same color. The one with the white background was the slowest to get started with the color change, by a half hour or so, but once they were all changing color, both of the DIY ones ended up with the green color at about 2 hours. Now, I'm not sure what affects the response time of these, but I am sure that both of these DIY designs work well. (Both of these have been spoken for now. Maybe someone else would like to start making these and selling them here?)


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## redstrat

Hoppy just currious, whats the cost range for one of your DIY drop checkers???


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## hoppycalif

davis.1841 said:


> Hoppy just currious, whats the cost range for one of your DIY drop checkers???


The cost of making one of these is hard to say. Tap Plastics, or at least my local store, won't sell small pieces of acrylic tube, so I bought 5 foot long pieces, which are about a dollar per foot. The little acrylic disks are about 50 cents each. And the cement is a few dollars for a tube big enough to make a hundred or more of these little things. The suction cups are "Lee's Heater Holders", two per package and a couple or so dollars for the package. I didn't have disks to fit inside the 1" dia tube, so I used a 1" hole saw to cut out pieces of 3/16" acrylic for those, since they needed a hole down the middle anyway. The cost of that is as near zero as you can get. I'm guessing my cost for each of these would be around $3. When I get thru with these, probably tomorrow, I will give them away for the $4.50 cost of priority mail plus PayPal fee plus $3 for the materials - $7.50, and one has already been spoken for. The Red Sea version on EBay just went for $14 including shipping, so this is still a bit cheaper, especially if you already have a pH test kit, and it's a lot cheaper if you make your own. (Providing you have a use for the left-over tubing and cement.)


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## fredyk

Hi Hoppy,
thanks for offer-taken you up on it. Tried to make one over the gas stove burner. beginners luck- it sort of worked, but the glass elbow broke. two more attempts did not succeed.
Mark


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## turbowagon

I thought of a situation where these drop checkers could potentially indicate a higher concentration of CO2 than is in the tank, when using a CO2 mist application.

Suppose the mist bubbles accumulate a little pocket of CO2 in the air chamber of the drop checker. If these bubbles are accumulating faster than they can dissolve, there will be an artificially higher concentration of CO2 in that little air pocket than in the rest of the tank. Since the little chamber of water in the drop checker is very small, the CO2 levels will become in equilibrium with the air pocket a lot faster than with the tank.

A way to test this hypothesis would be to surround the drop checker with a shield that prevents the mist bubbles from entering the chamber and seeing if the indicated CO2 level changes.


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## Fome

davis.1841 said:


> Hoppy just currious, whats the cost range for one of your DIY drop checkers???


Mine cost about $1 for the container.

Suction cup, cement, and ph indicator wasn't included in price, however because I had all those things on hand.


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## hoppycalif

turbowagon said:


> I thought of a situation where these drop checkers could potentially indicate a higher concentration of CO2 than is in the tank, when using a CO2 mist application.
> 
> Suppose the mist bubbles accumulate a little pocket of CO2 in the air chamber of the drop checker. If these bubbles are accumulating faster than they can dissolve, there will be an artificially higher concentration of CO2 in that little air pocket than in the rest of the tank. Since the little chamber of water in the drop checker is very small, the CO2 levels will become in equilibrium with the air pocket a lot faster than with the tank.
> 
> A way to test this hypothesis would be to surround the drop checker with a shield that prevents the mist bubbles from entering the chamber and seeing if the indicated CO2 level changes.


That is a potential problem, but I don't see it as a serious one. These things reach equilibrium pretty slowly, over a couple of hours, or so. So, unless there is a steady stream of CO2 mist bubbles gathering under the "horn" of the device, then dumping their remaining CO2 into the air gap, all that should happen is that the indicator will "overshoot" the true CO2 value, but settle down to an accurate reading eventually. If the ppm of CO2 in the bulb of the device is above that in the water, the CO2 will migrate back to the tank water.

I think the problem can best be avoided by choosing a good location to mount the device - where there is good water circulation, and at the opposite end of the tank from any mist generation. Those CO2 micro bubbles can't exist for very long in the water, before the CO2 diffuses into the water, leaving a microbubble of other gases. So, I suspect that most of the bubbles are "inert" by the time they are swirling around the opposite end of the tank.


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## Minsc

For those of you who don't mind your D.I.Y. being a bit U.G.L.Y.,
I present: the rigid airline "M"









Cap one end of the airling with masking tape, fill it with salt to within a half inch of the top, cap the other end, put it in a vice, apply heat via hairdryer, bend.

It aint pretty, but it didn't cost me a thing, and I don't plan on keeping it in the tank for very long


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## hoppycalif

That certainly looks effective if not beautiful. And, if you only want to verify that your bubble rate is giving you the amount of CO2 you desire, this should work perfectly. Hey, maybe we could get Home Depot to buy a few of the ADA ones for their tool rental department?

For those who don't read many other aquatic plant forums, Tom Barr did some experimenting with this device and came up with the idea that you could get rid of the air gap entirely, and speed up the response rate considerably, just by using a gas permeable membrane to hold the reference KH solution. Then, if that membrane is in the form of a stocking over the business end of a pH probe, you have a CO2 probe - with fast reaction and great accuracy. He has done a prototype, of sorts, and it works. And, he is working towards getting this available for all of us.


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## fredyk

This drop checker, from you, works really well, hoppy, thanks.
Mark


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## schaadrak

Tyvek (the stuff they wrap houses with before they add the siding) is a gas permeable membrane that is pretty much available anywhere. I've only seen it sold in the big rolls, but if there's any new houses being built around, your sure to find scraps of it.

I remember I worked for a place that sold raincoats made out of Tyvek. The company gave us a display that was a clear cylinder with a sheet of it in the middle dividing it in two. Water was poured into the top chamber and an air pump was connected to the bottom chamber which forced air through the Tyvek and up through the water. Even while the pump was off there was never any water in the bottom chamber.


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## hoppycalif

schaadrak said:


> Tyvek (the stuff they wrap houses with before they add the siding) is a gas permeable membrane that is pretty much available anywhere. I've only seen it sold in the big rolls, but if there's any new houses being built around, your sure to find scraps of it.
> 
> I remember I worked for a place that sold raincoats made out of Tyvek. The company gave us a display that was a clear cylinder with a sheet of it in the middle dividing it in two. Water was poured into the top chamber and an air pump was connected to the bottom chamber which forced air through the Tyvek and up through the water. Even while the pump was off there was never any water in the bottom chamber.


Now that is a creative burst of inspiration!! I should be able to find some scraps of Tyvek, and I had forgotten completely that it is a semipermeable membrane, and a very rugged one at that. If I can find some scraps at Home Depot, for example, I will try to make a KH reference "condom" for my pH meter and see how it works. THANK YOU!! If you also post at Tom Barr's forum I suggest you post this there. If I don't see it in a day or two I will post the idea myself.


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## redstrat

Hoppy do you have any more of the Drop checkers you built that you were selling??? I'd be really interested in buying one from you.


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## hoppycalif

davis.1841 said:


> Hoppy do you have any more of the Drop checkers you built that you were selling??? I'd be really interested in buying one from you.


No, I only built two, just to demonstrate that you can easily make one and it works well. I was also trying to see which configuration would work best. I may make a few more sometime, but it isn't likely, and I don't want to do this for profit. I do have a big hunk of 1" acrylic tube and 5/8" acrylic tube left over, if someone wants some. I could easily cut it into 8 inch pieces and ship that by priority mail, but you would still need to buy from somewhere a tube of medium viscosity acrylic cement and a small scrap of thin acrylic plastic.


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## redstrat

thats ok hoppy, I just thought you were making a few extras before.. no problem. I dont have the time to DIY one myself right now so I'll probably just pay the extra for the e-bay ADA look alike version. although, I may have time in a couple weeks to build one diy... we'll see.


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## schaadrak

hoppycalif said:


> Now that is a creative burst of inspiration!! I should be able to find some scraps of Tyvek, and I had forgotten completely that it is a semipermeable membrane, and a very rugged one at that. If I can find some scraps at Home Depot, for example, I will try to make a KH reference "condom" for my pH meter and see how it works. THANK YOU!! If you also post at Tom Barr's forum I suggest you post this there. If I don't see it in a day or two I will post the idea myself.


You're welcome and post away. I barely have time to post in this forum.


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## redstrat

hoppycalif said:


> Dennis, how did you seal around the probe, to keep the air from leaving the drop checker? Incidentally, you beat Tom Barr to this! He has been posting about making one of these by mid December. The only non-fool-proof part of this design that I see is the electrical interferrence issue. How do you satisfy yourself that the probe is not being affected by interferrence?


I just came across this little part that sounds like its made for a situation just like this. Check it out.

Also does anybody know what kind of indicator solution is used in the Red Sea Drop Checker/"Co2 Indicator"????


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## caymandiver75

davis.1841 said:


> I just came across this little part that sounds like its made for a situation just like this. Check it out.
> 
> Also does anybody know what kind of indicator solution is used in the Red Sea Drop Checker/"Co2 Indicator"????


Isn't it bromthymol blue?


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## hoppycalif

As best I can determine, bromothymol blue is the only pH indicator dye that gives yellow to blue readings, that is used in such test kits. There are a few others that give different colors, and for differenct pH ranges, but not for yellow to blue.


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## redstrat

Thats what I thought but figured I'd ask to be a little more confident with that assumption. Thanks

I just bought one of the Red Sea versions of the drop checker and I love it. I would almost consider a drop checker to be a must have item for anybody trying to get the most out of DIY Co2. I really like being able to adjust the "good" color to match the CO2 concentration I'm trying to achieve.


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## caymandiver75

davis.1841 said:


> Thats what I thought but figured I'd ask to be a little more confident with that assumption. Thanks
> 
> I just bought one of the Red Sea versions of the drop checker and I love it. I would almost consider a drop checker to be a must have item for anybody trying to get the most out of DIY Co2. I really like being able to adjust the "good" color to match the CO2 concentration I'm trying to achieve.


Cool. I also have that Red Sea version drop checker and last night got some distilled water and baking soda and got the kh to 4. Place the drop checker back in the aquarium and within 2 hrs it went from Blue to Very very light green almost yellow.


----------



## jolywoo

I use the redsea version too with distilled water set to kh of 5. Looks like you have a good co2 in your water, even all the bba on your driftwood is gone.


----------



## caymandiver75

jolywoo said:


> I use the redsea version too with distilled water set to kh of 5. Looks like you have a good co2 in your water, even all the bba on your driftwood is gone.


Hehe yeah the BBA is gone because I took about an hour to scrape off all the algae, trim the plants that had it, etc. What a pain in the butt! Now that my water conditions are checked and I reduced my lighting I'm hoping the stuff never grows back. What little is left i'm praying my 6 Oto's will take care of.


----------



## Naja002

hoppycalif said:


> For those who don't read many other aquatic plant forums, Tom Barr did some experimenting with this device and came up with the idea that you could get rid of the air gap entirely, and speed up the response rate considerably, just by using a gas permeable membrane to hold the reference KH solution. Then, if that membrane is in the form of a stocking over the business end of a pH probe, you have a CO2 probe - with fast reaction and great accuracy. He has done a prototype, of sorts, and it works. And, he is working towards getting this available for all of us.


I would imagine, for testing purposes, that the "Breather Bags" that people use to ship fish in would work for a membrane--The Bag--let's C02 Out--Oxygen In. Reversed (into/toward the Drop checker): its should let the C02 In. But will it let it back Out to maintain equilibrium? Hmmmmmmmm.....

Needing one clarification: Drop Checker fluid--set to Kh 5 will read the same C02 ppm as what is in the Tank? Meaning regardless of tank Kh (2, 6, 8, 12 whatever) the ppm of C02 in the tank will match the Kh4 Soultion? I can almost grasp that, but it just doesn't seem right....... I looked at the "Table" posted:

Table Link

And I'm just missing something. I'll re-read that a couple dozen more times and see if I can get it to "Click"........:rofl:

Thanx!


----------



## redstrat

how the Distilled water with an adjusted KH works is this,
in the drop checker the solution will match the dissolved CO2 of the aquarium regardless of KH in either solution. Knowing this, we add an indicator such as Bromethyl blue(not sure about the spelling) that will show certain colors at a known PH. Using this we can adjust the PH of the indicator solution in the drop checker to change the color to green at the desired concentration of CO2 by manipulating the KH. for example a KH of 4 in the distilled water bromethyl blue solution will be green when the CO2 is at 30ppm, regardless the water chemestry in the aquarium. the whole point of this is to narrow the margin of error in our CO2 measurements. 

Correct me if I'm wrong but by adjusting the KH in the solution what CO2 concentration will show green in the following using bromethyl blue indicator and distilled water and the KH adjusted using Baking Soda:
KH3 Green = 20ppm CO2?
KH4 Green = 30ppm CO2
KH5 Green = 40ppm CO2?

These are all +/- 5ppm, correct?

I'm not sure about exact numbers here but i know qualitativly this should be correct I hope it helps clear some things up.


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## caymandiver75

Yeah according to Hoppy on the 1st page.

"Here are the color charts for the three commonly used pH test kit reagents. For the top one, it is yellow at pH of 6.0, blue at 7.2, and green (the middle) at 6.6."

You can verify this by plugging in the KH and respectable PH into the following calculator to verify your results. CLICK HERE


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## Naja002

Ok, Thanx. I understand what You are saying and I actually was typing out a response when I think it clicked. So, let me see if I have this right:

X-amount of C02 will create X-ppm regardless of Kh.

The Higher the Kh--the more C02 it will take to create X-amount of change in pH.

*BUT,* since we are not concerned with the pH in the Tank--it becomes irrelevent. The focus is on the pH change in the Drop-Checker because 30ppm is 30ppm--regardless of Kh, Correct?

If we matched the Kh to that of the Tank--then we would just be chasing the "Color Scale" and making it more difficult, Correct?

I think I've got it--just need confirmation.....


----------



## caymandiver75

Naja002 said:


> Ok, Thanx. I understand what You are saying and I actually was typing out a response when I think it clicked. So, let me see if I have this right:
> 
> X-amount of C02 will create X-ppm regardless of Kh.
> 
> The Higher the Kh--the more C02 it will take to create X-amount of change in pH.
> 
> *BUT,* since we are not concerned with the pH in the Tank--it becomes irrelevent. The focus is on the pH change in the Drop-Checker because 30ppm is 30ppm--regardless of Kh, Correct?
> 
> If we matched the Kh to that of the Tank--then we would just be chasing the "Color Scale" and making it more difficult, Correct?
> 
> I think I've got it--just need confirmation.....


I'm in the same boat. I'm sure someone will come here and give us confirmation. Taking a look at this chart that is from the same page as the CO2 calculator link in my previous post it does appear that the higher the Kh--the more C02 it will take to create X-amount of change in pH.


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## Naja002

True, but that is the kicker, I think:

X-amount of change in *pH*......

*PPM* stays the same though.....and that's what we are after....

Provided I am finally seeing this correctly!

Question:

I have made a DIY Drop Checker. It is bulky and I will post pix shortly. RODI Water set to 5Kh---How Much/Many pH drops do I add? Does it Matter? Do I need to measure the solution going into the Drop Checker and add 3 drops/5ml (AP Test Kit)?

Thanx!


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## hoppycalif

I experimented with the AP test kit, adding varying amounts of the pH reagent to tubes with the same water - tank water - in them. It made no difference to the results whether I used the three drops the instructions call for, or 2 or 6 or even 9 drops. With larger numbers of drops the result becomes a murky opaque liquid, where reading the color is harder, not easier. But, the color stayed the same for all. So, I just add whatever amount makes it easiest to judge the color.


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## Naja002

Hi Hoppy,

Thanx for the Clarification. I found the answer from some previous posts of Your's here:

DIY Drop Checker--Post #1

Which leads to here--More in-depth:

 Does it work? ADA glass dropcheck co2 indicator--Post #25

Here's some Pix of the 1 I just made--Mind you, its cost was $0 (I had everything) and it's going into my A. javanicus setup--so, looks are not currently of utmost importance:

Parts:










Assembled--the top heater holder just goes above the bottle to help reduce the buoyancy-pull on the heater holder around the bottle neck:










Full:










Its an 8.45 Fl oz. "Kid's Connection Soda" bottle. I bought them at Walmart in a 4-pak for $1-2 and I use them for DIY C02 Bubble Counters. This one was an Extra. The PVC is just 1/2" and the bottle opening fits it like a glove--No glue, silicone, etc. It currently has about 95ml of RODI water set to 5kh w/ BS.

I added 114 drops of pH liquid--and its really too dark. I am going to install it an see how it looks under the light. But I will probably redo it with less drops. The water color is not Blue, but Blue-green--what does that mean? The RODI water was made yesterday and was putting out 0-2ppm TDS. The Gallon jug has just be sitting capped overnight. Any thoughts on that?

*EDIT:* I was afraid that the bottle body was just going to be too wide for the suction cup to hold--and it is. So, I have eliminated the suction-cups and tied 2--1 1/2 oz lead weights around the neck--dangling about 3" below the bottle. So, now it is a floating version. :-\"

Anybody know if the entire Drop Checker *Must* be below the water surface--like for pressure? I guess we'll find out in a few hrs!

I also redid the fluid mixture: 100ml and 10 drops of pH liquid. Now its a nice pretty blue and should be easy to read....

Thanx!


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## hoppycalif

The reason for keeping the entire device under water is to avoid any temperature difference between the device and the tank water. If there is a difference some distillation will occur - water will migrate from the warmer to the cooler area, which changes the KH of the tester water. 

Are you sure there is no leakage between the pvc tube and the bottle neck? If so, that has to be the easiest one yet to make. (But not the most unobtrusive or most elegant or coolest!)


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## Naja002

> Are you sure there is no leakage between the pvc tube and the bottle neck?


Absolutely? Positively? Well, No, but as You can see in the pic above--there is no leakage onto the Towel. And in order to get the PVC pipe back out--I have to insert my finger, bend it to kind of Lock it in place, and fight and struggle for a bit. I can't guarantee that there will not be any osmosis at all, but its a solid fit. Time will tell, I guess!

I just got the fishing line back out and tied it to a rock that will reach the bottom yet keep the Checker below the surface. Its in my Plant Filter, so looks really isn't a Big Deal. Ghetto? Yes, but if it provides some benefit--I'll do it right later...After 4hrs of floating--the color didn't change at all (floating). According to the Chart: I have pH 6.0, Kh 2, so C02 should be around 60ppm. We'll see if the color changes now that its completely submerged.

Thanx!


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## schaadrak

Just a thought, but if the membrane idea pans out, these could be made even easier by gluing a piece of membrane to the top of any small clear container filled with indicator solution.

Like this:










It wouldn't matter which way was up since water can't go through the membrane and you could use any small clear container you have lying around with virtually no modifications. Heck, you could just glue membrane to either side of a piece of air line tubing. Then if it starts going bad, toss it out and throw a new one in.


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## hoppycalif

schaadrak said:


> Just a thought, but if the membrane idea pans out, these could be made even easier by gluing a piece of membrane to the top of any small clear container filled with indicator solution.
> 
> Like this:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> It wouldn't matter which way was up since water can't go through the membrane and you could use any small clear container you have lying around with virtually no modifications. Heck, you could just glue membrane to either side of a piece of air line tubing. Then if it starts going bad, toss it out and throw a new one in.


As I recall, the membranes are made of teflon or polypropylene plastic, and neither of those is at all easy to glue. Both are, I think, considered "release agents". If you can use glue, I hope someone with the knowledge will tell us which glue to use. If I had some membrane, other than Tyvek, which is very thick and stiff for something like this, I would just wrap it around a piece of tubing and rubber band it in place. I do have a pretty nice piece of transparent vinyl 1/2 inch tubing I could easily use this way. But, the first steps are to find a source of membrane, and to find out if there is a glue that will work with it.

EDIT: I did some googling and found the obvious source of membrane material - Kordon breather bags! Who has some and is willing to supply one or two to me - of course I will pay shipping and cost of the bag(s)?

EDIT AGAIN: It only took a few minutes to get two offers of these bags, and both are relatively local to me! If I can make this work out I will make two or three extras and offer them to whomever wants them. But, I hope someone else tries this idea too.


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## epicfish

hoppycalif said:


> EDIT: I did some googling and found the obvious source of membrane material - Kordon breather bags! Who has some and is willing to supply one or two to me - of course I will pay shipping and cost of the bag(s)?


Naja002 suggested breather bags already: http://www.aquaticplantcentral.com/...checker-14.html?highlight=breather#post256349

=P

I think, for an effective drop checker using a semi-permeable membrane, you could overfill a test tube or container or whatever, and place the membrane over the top so that there is absolutely no air inside the container. This way, the dissolved CO2 within the tank can directly dissolve through to the other side and give faster results.

Of course, since CO2 in H2O yields carbonic acid, I wonder if these molecules will be able to get through the membrane...no time to ponder this for now. Final exam in 2 hours.


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## Naja002

The Breather bags are designed to let C02 out and 02 in--question is: does it go both ways?

In order to maintain equilibrium the C02 must be able to enter and exit as it changes in the tank. Guess that would be a question for Kordon.

My Ghetto Drop Checker changed colors since I completely submerged it. Its Green now, but hard to tell *Which* Green!  I guess I'll add a few more drops of the pH liquid and see if that helps.....


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## hoppycalif

The reason the Kordon bags "let oxygen in and CO2 out" is the same reason it will work for the drop checker. The gas will always reach equilibrium conditions on each side of the membrane. So, if the fish or plants are using O2, the O2 concentration will drop on that side of the membrane and O2 will have a net inflow to that side. But, if the fish or plants release CO2, the CO2 concentration will increase on that side and there will be a net outflow of CO2. The membrane is little more than a net with extremely small openings, so it must be able to let gases go either direction.

If I were designing a membrane drop checker for sale, I would have a sheet of membrane with 4-5dKH water and pH reagent spread on it, lay a second sheet on top, then heat seal a grid of 1" squares, so it separates into a bunch of 1" square pillows with standard KH water/reagent sealed inside. One of these could just float in the aquarium - it would have near neutral buoyancy.

So, who has a machine that does this - seals two heat sealable plastic sheets together in 1" squares? Surely one of us has one hidden away in the garage??


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## redstrat

EDIT: opps didn't see hoppy's post please ignore this, I just repeated what he said basically.


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## Naja002

Makes sense. I just never really thought about it. The description that I read--probably a yr ago--basically said that it let's C02 Out and 02 in because of the pore size. But I guess what they were really getting at is: because the the pore size--it allows the gas exchange _while keeping the Water in!_



> If I were designing a membrane drop checker for sale, I would have a sheet of membrane with 4-5dKH water and pH reagent spread on it, lay a second sheet on top, then heat seal a grid of 1" squares, so it separates into a bunch of 1" square pillows with standard KH water/reagent sealed inside. One of these could just float in the aquarium - it would have near neutral buoyancy.


Sounds like a New Product for Seachem! Like their pH and Ammonia Alerts.....

Probably not much help, but: the Vacuum packers they sell at walmart, etc have a heat sealer for those types of plastic bags. If you know someone that has one........Maybe you could borrow it.


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## kamel_007

hoppycalif said:


> Is that a shot glass? How did you make it? Once you understand how simple this device is, there must be a dozen ways to make one. The absolute simplest I have heard yet is to take a plastic tube, bend it into a "U" shape and cap one end. Of course a suction cup is still needed, but there are lots of options for that too.


what do you mean with a shot glass??

it's just a small cup..


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## hoppycalif

epicfish said:


> Naja002 suggested breather bags already: http://www.aquaticplantcentral.com/...checker-14.html?highlight=breather#post256349
> 
> =P


Yes, and I completely missed that. I was obsessed with how to make a container that I could easily replace the membrane on at that time, not the membrane itself. It is still a great idea, and a really cheap source for membrane materials.


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## hoppycalif

kamel_007 said:


> what do you mean with a shot glass??
> 
> it's just a small cup..


The photo looked like the bottom of the cup was thick like a shot glass is made, so I just thought it would be a good joke! I keep being amazed at the variety of ways there are to make this little device. When I first thought seriously about it I assumed that the ADA type glass device was the only good idea - now we are down to a piece of tubing, a piece of breather bag and a rubber band!


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## dennis

I'm not so sure the breather bag idea works. I've had a couple differnt models in my tank for over an hour and there is no color change.


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## junco

Sorry if this has been brought up already, but I didn't have time to read the 15 pages of this thread 

If I didn't want to take the time to construct one of these, or buy one... and just wanted to do a quick test to see if my KH/pH chart method is fairly accurate, could I do the following?

1) Take a piece of tubing and seal it at one end and bend it in a U shape.
2) Use syringe/pipette to put distilled water into one end of the U and secure underwater in tank somehow.
3) Let sit overnight, take out next day during peak light hours when respiration is moving right along.
4) Test the pH and KH of this water and compare to the chart to get current CO2 level.

Would this work? I don't really need a day by day view of this and just want to see if the pH/KH chart method is accurate enough for my needs. I wouldn't need to buy anything, construct anything, or spend an hour getting distilled water to be exactly 4 KH.


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## hoppycalif

If you are going to use pH reagent to find the pH of the water you need to adjust the KH of the water to around 4 or 5 dKH, assuming you will be measuring around 30-40ppm of CO2. The color is just too hard to judge accurately unless you are reading about 6.6 pH. And, plain distilled water won't work because it has no measurable KH, so it gives an ambiguous reading of CO2. But, the device you describe will work fine.


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## hoppycalif

dennis said:


> I'm not so sure the breather bag idea works. I've had a couple differnt models in my tank for over an hour and there is no color change.


Dennis, this idea has to work doesn't it? Assuming the breather bags really do allow CO2 and other gases to pass thru freely? The time it takes for them to reach equilibrium might be long, but I don't see how they can fail to work eventually. Tom Barr believes a device like this will have a short response time, but I haven't seen any data to say, one way or another. Of course a breather bag, used for its intended purpose, doesn't need to react very quickly. So, it is possible that the density of the pores in the bag material might be too small for the material to work rapidly for this.


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## dennis

I think Tom is getting that notion from the fact that he plans to use DO probe membranes. The DO probe has a fast response time and works basically exactly like he has described in his posts. As usual though, I don't follow his notion of cheap since I can't find any that are less than ~$25 per membrane. I obviously don't know where he is looking as he never tells....

The breather bags should work in theory though don't know exactly how they work. There might be an issue with pressure across the gradient, or lack of with water on both sides. I really don't know much about osmosis type functions, other than the basics of things wanting to be at equilibrium. 

I'll let them float around longer. It is possible that there is to large an air space above the indicator sample. Let me say what I did... I took a small specimen jar with a snap on lid, about 10ml volume. I cut away most of the lid leaving only the outer rim. Placed a small piece of Kordon bag over the opening and snapped on the lid rim. Works great. The hole in the lid is about 1/2" diameter. I added 1ml to this and placed it inverted in the aquarium so that the indicator solution is sitting on the Kordon. I also made another that has a 3/16 hole but the container is 7ml and I used 2ml of solution. This one is tall and skinny compared to the first with is shorter and wider. Neither is showing a color change after ~3hrs.


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## Naja002

Might sound Crazy, but before you give up---how about flipping the membrane around and trying it that way?

Maybe they only let 02 in and C02 out--who knows?  

If it works after flipping--I would say the it won't maintain equilibrium, but would be like a one time reading.......Hope that makes sense.....


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## hoppycalif

dennis said:


> I think Tom is getting that notion from the fact that he plans to use DO probe membranes. The DO probe has a fast response time and works basically exactly like he has described in his posts. As usual though, I don't follow his notion of cheap since I can't find any that are less than ~$25 per membrane. I obviously don't know where he is looking as he never tells....
> 
> The breather bags should work in theory though don't know exactly how they work. There might be an issue with pressure across the gradient, or lack of with water on both sides. I really don't know much about osmosis type functions, other than the basics of things wanting to be at equilibrium.
> 
> I'll let them float around longer. It is possible that there is to large an air space above the indicator sample. Let me say what I did... I took a small specimen jar with a snap on lid, about 10ml volume. I cut away most of the lid leaving only the outer rim. Placed a small piece of Kordon bag over the opening and snapped on the lid rim. Works great. The hole in the lid is about 1/2" diameter. I added 1ml to this and placed it inverted in the aquarium so that the indicator solution is sitting on the Kordon. I also made another that has a 3/16 hole but the container is 7ml and I used 2ml of solution. This one is tall and skinny compared to the first with is shorter and wider. Neither is showing a color change after ~3hrs.


With the air space sitting above the KH standard solution it will moderate the change in ppm of CO2 in the KH liquid. The air space has to reach equilibrium with the KH liquid as the KH liquid is reaching equilibrium with the tank water.  So, wouldn't that just slow down a regular drop checker even more? By forcing the tank water CO2 to go thru the membrane holes instead of through a big air/water interface? I'm still betting that eventually the color will change as expected. And, intuitively I would say the smaller the quantity of KH water divided by the area of the membrane, the faster it could react. So the ideal would be a .030 thick layer of KH water with a membrane on both sides having a square inch of area. I haven't made any effort to prove this, nor do I know how to start to do so, but if I get bored I will make the attempt, at least to do it with a mind experiment.


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## epicfish

Wouldn't something like the Vacuum Sealer work? Do they seal with heat?

Of course, you'd have to trick the machine into thinking that there was suction before the bag was sealed.


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## dennis

Naja002 said:


> Might sound Crazy, but before you give up---how about flipping the membrane around and trying it that way?
> 
> Maybe they only let 02 in and C02 out--who knows?
> 
> If it works after flipping--I would say the it won't maintain equilibrium, but would be like a one time reading.......Hope that makes sense.....


I tried that when there was no change after about 2 hours


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## hoppycalif

Dennis, do you have anything new to report on your testing with Kordon breathing bags? I just got a few from Bill Harada to play with, and the first things I notice are that the bags are covered with lots and lots of writing, part of that writing says it doesn't work under water. That surprises me, and I don't really believe it. If a gas can pass from the air to the water and from the water to the air, I can't see a physical reason it can't pass from water to water. I plan to try a simple experiment to verify that.

Meanwhile, over on Tom Barr's forum, Tom says the bags will have such a slow response time they will not work. That doesn't surprise me too much, since the original purpose for the bags doesn't require much of a response time. Fish just don't breathe a whole lot of O2 in and CO2 out - they are kinda small. But, for a DIY drop checker, a fast response time isn't all that important either. Response time is only important if you are using this for lab experiments of some kind and want to see the effect of a change fairly quickly. (In my opinion.)


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## dennis

It does work but takes about 24 hours to get to equilibrim. It also never gets to the same color as my regular open end drop checker. The small holed unit never changes color and the one with 1/2" opening gets blue-green while the other, regular style is green/yellow.

The response time is actually so slow that it won't even stabalize over the photoperiod. 

I still can't find a source for the Teflon Tom talks about. Ican find them listed but no prices or avialibility for seperate ordering. I wonder if by the time one goes through the 5 disks normally included with a DO probe that the probe needs to ba replaced as well. I see proces for the probes ~120. I don't know exactly what the membranes are made from, other than Teflon of which there are lots of types and thicknesses. I have seen the membranes listed as 1mm and .1mm but I assume they must be .1mm. I searched for .1mm Teflon sheet/film but there were lots of options of types, porosity, etc.


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## hoppycalif

Back to the drawing board I guess. I still plan to try one of the breathing bags to see what I can find out, and I have a small piece of Tyvek to try the same way, not that I expect it to work at all. 

I have been doing a lot of google and wikipedia research on gas permeable membrane and I have learned that I know nothing whatever about the subject. That is a challenge!


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## epicfish

American Chemical Society Publications: Authorization Required

Read through it. "Sensors for CO2 and Dissolved Organics in Water." using Teflon 1600/2400 AF (amorphous fluropolymer).


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## epicfish

Permeability of Co2 in Amorphous and Crystalline Teflon Membranes

Permeability of Co2 in Amorphous and Crystalline Teflon Membranes

Teflon 2400 membranes are apparently the best.


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## epicfish

Fluoropolymer carbon dioxide sensor

Fluoropolymer-based capacitive carbon dioxide sensor

That's for air w/o H2O vapor.


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## epicfish

I am highly doubting the purchase of Teflon AF for aquatic purposes.

Shop Teflon - Your Source for Industrial Teflon® Products


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## epicfish

DuPont Teflon AF fluoropolymer resins

Also: "
U.S. customers can shop our online Teflon® Store for Teflon® AF.
Note: You must have a License Agreement on file to purchase Teflon® AF."


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## Naja002

Won't hurt to write the various companies, including DuPont, and ask for a "Sample".


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## hoppycalif

Dupont is selling samples of this material for $500 to $1000! Now, I don't mind spending $10 now and then just to experiment with, but that's about tops for me.

I am continuing to read up on gas permeable membranes, and I notice that silicone rubber is a good material for CO2 permeability, but I don't see where one could obtain thin sheet silicone rubber. And, I saw a hint that latex rubber also is gas permeable - which (blush) leads me to wonder about using condoms, the extra thin kind. Does that sound promising to anyone?


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## dennis

Tom said the stuff is cheap. I don't think he would be messing with it as a realistic thing for the hobby if it were not. Obviously we are not looking into the same sources as he is. This Teflon stuff you finding now is pretty new but DO probes have been around for ages. We're just not looking in the right places.

Don't you just love how he always wants to help but will never really share the important stuff?


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## dennis

Here we go. Looks like about ~$1 per membrane. still don;t know what they are made from though.

YSI Meter Accessories And Replacement Membrane Kits - Cole-Parmer Catalog


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## hoppycalif

I found CO2 probes of this type already exist for blood gas analysis. They have a gas permeable membrane with a carbonate/distilled water solution between the membrane and the pH sensor, just as Tom is proposing. Looks like once again someone has figured it out before us, and probably patented the design.

The Cole-Parmer membranes are intriguing, and I may decide to buy a package of them just to play with. But, the season, the other jobs (making a Murphy bed, producing two newsletters, finding a new camera, etc.) are interfering right now. I'm still wondering if an ordinary condom acts as a gas permeable membrane.


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## dennis

Hoppy, your idea probably is not cheaper. I also hope they are not very permeable. I know gas molecules are pretty small but still....


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## schaadrak

hoppycalif said:


> I am continuing to read up on gas permeable membranes, and I notice that silicone rubber is a good material for CO2 permeability, but I don't see where one could obtain thin sheet silicone rubber.


What about some thin, clear, silicon rubber tubing?

Some other avenues to explore are Gore-Tex and SympaTex, both relatively common fabrics. I think eVent is another brand, but I'm not sure.


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## hoppycalif

I haven't found a source of thin silicone rubber tubing. The stuff we sometimes use for CO2 tubing is too thick and too opaque - mine is blue also. The secret of all of this is to find consumer products that use what we are looking for, so the price is reasonable. I'm still thinking about the Cole-Parmet membranes, and I did sign up with their web site.

Edit: I bit the bullet and purchased a pack of the membranes. It's my Christmas present to myself!


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## epicfish

hoppycalif said:


> I found CO2 probes of this type already exist for blood gas analysis. They have a gas permeable membrane with a carbonate/distilled water solution between the membrane and the pH sensor, just as Tom is proposing. Looks like once again someone has figured it out before us, and probably patented the design.


Some has figured it out before us? That might be quite an underestimation.

This is a list of references from an article I found dealing with a probe-type detector for real-time PCO2 and PO2 in patients. Notice many of these publication dates are least 20 or 30 years old.

References

Bruggen van and Scott, 1962. J.T. Bruggen van and J.C. Scott , Microdetermination of carbon dioxide. Anal. Biochem. 3 (1962), pp. 464-471.

Eigen et al., 1961. M. Eigen, K. Kustin and G. Maass , Die Geschwindigkeit der Hydratation von SO2 in wässriger Lösung. Z. Physik. Chem. (N.F.) 30 (1961), pp. 130-136.

Gibbons and Edsall, 1963. B.H. Gibbons and J.T. Edsall , Rate of hydration of carbon dioxide and dehydration of carbonic acid at 25.0 °C. J. Biol. Chem. 238 (1963), pp. 3502-3507. Abstract-MEDLINE

Harned and Scholes, 1941. H.S. Harned and S.R. Scholes, Jr. , The ionization constant of HCO2−3 from 0 to 50.0 °C. J. Am. Chem. Soc. 63 (1941), pp. 1706-1709. Full Text via CrossRef

Harned and Davis, 1943. H.S. Harned and R. Davis, Jr. , The ionization constant of carbonic acid in water and the solubility of carbon dioxide in water and aqueous salt solutions from 0 to 50.0 °C. J. Am. Chem. Soc. 65 (1943), pp. 2030-2037. Full Text via CrossRef

Jones and Bradshaw, 1933. G. Jones and B.C. Bradshaw , The measurement of the conductance of electrolytes.V. A redetermination of the conductance of standard potassium chloride solutions in absolute units. J. Am. Chem. Soc. 55 (1933), pp. 1780-1800. Full Text via CrossRef

Kempen van, 1972. L.H.J. Kempen van , Estimation of free and hemoglobin-bound CO2. Thesis (1972) Nijmegen .

Kempen van et al., 1972. L.H.J. Kempen van, H. Deurenberg and F. Kreuzer , The CO2-quinhydrone electrode. A new method to measure partial CO2 pressure in gases and liquids. Respir. Physiol. 14 (1972), pp. 366-381.

Lunn and Mapleson, 1963. J.N. Lunn and W.W. Mapleson , The Severinghaus PCO2, electrode; a theoretical and experimental assessment. Brit.J. Anaesthesiol. 35 (1963), pp. 666-678.

Maffly, 1968. R.H. Maffly , A conductometric method for measuring micromolar quantities of carbon dioxide. Anal. Biochem. 23 (1968), pp. 252-262. Abstract

Murakami et al., 1965. I. Murakami, S. Takashima, K. Fujisaku, H. Sasamoto, Y. Takagi and Y. Oota , A new method for determination of PCO2, both in liquid and gas. In: Digest 6th Internal. Conf. Med. Electron. Biol. Engin. (1965), pp. 610-611.

Robinson and Stokes, 1959. R.A. Robinson and R.H. Stokes , Electrolyte Solutions. , Butterworths, London (1959).

Stow et al., 1957. R.W. Stow, R.F. Baer and B.F. Randall , Rapid measurements of the tension of carbon dioxide in blood. Arch. Phys. Med. Rehabil. 38 (1957), pp. 646-650. Abstract-MEDLINE

Taylor, 1953. G. Taylor , Dispersion of soluble matter in solvent flowing slowly through a tube. In: Proc. Roy. Soc. A 219 (1953), pp. 186-203. Full Text via CrossRef

Tsao and Vadnay, 1964. M.U. Tsao and A. Vadnay , A method for continuous measurement of blood PO2, and PCO2. J. Lab. Clin. Med. 63 (1964), pp. 1041-1053. Abstract-MEDLINE


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## epicfish

Measurement of ASL pH. We developed a novel technique to measure pH with pH-sensitive microelectrodes (Microelectrodes, Bedford, NH) in small-volume samples that could be quickly temperature, water vapor, and gas equilibrated. Microaliquots (0.3-1.0 µl) were aspirated from the microcapillary tube into the tip of a section (0.5 cm) of CO2-permeable silicone tubing (Helix Medical, Malvern, PA; 0.025 in inner diameter, 0.047 in outer diameter). The pH microelectrode was inserted into the sample by stretching the end of the tubing containing the sample over the microelectrode tip, the tight fit trapping a thin layer of liquid between the tubing wall and the electrode, so that reference and pH electrodes made contact with the sample. The microelectrode and tubing were placed in a water bath that was continually gassed and equilibrated with 5% CO2. A column of air in the tubing, distal to the electrode, prevented water from reaching the sample. CO2 equilibration was complete within 2 min, as evidenced by a stable pH. Measurements were accurate and reproducible within ±0.01 pH units.

From: Abnormal surface liquid pH regulation by cultured cystic fibrosis bronchial epithelium -- Coakley et al. 100 (26): 16083 -- Proceedings of the National Academy of Sciences

And from Helix Medical: Standard Tubing Wacker
We have the same tubing as described within the article:
60-411-42 .025 .64 .047 1.19 .011 .28

CO2-permeable silicone tubing. Probably cheaper then $500 per sample.


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## Robert Arnold

Well, I recieved my Red Sea checker today. Unfortunately didn't have any distilled water left after making the last batch of CSM+B - and forgot to replace it. But there is a bypass on my well house's water conditioner and my KH is near zero there. 
So I thought I'd try a little experiment untill I get the distilled water. I used the well water and after adding a very tiny amount of baking soda, finally got a KH of 5 (after a few more trips to the well house). Put one ml. of the KH 5 water into the little Red Sea container. Next I added about 6 drops of AP pH test solution and it came out quite green. Oh well... I suppose there is a bit of CO2 acid in my well water which generally rises to a standing pH of 6.6 from pH 5.2 out of the tap. Tommorrow, with distilled water, I'm hoping I'll get the blue color as this method requires.

Is it possibly CO2 acids which caused the KH5 well water to be green from the get go??


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## hoppycalif

I don't think it is likely that well water will contain 40 ppm of CO2, and I know it won't if that water is allowed to sit in the open for very long. You just have to use either DI or distilled water for this method to be any better than just measuring the tank pH and KH.


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## dennis

The well water could contain a lot of dissolved gases from ground sources, pressurizing and pumping. There may be other reasons for your results but it is certainly possible to have lots of dissolved gases present in a freshly drawn sample.


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## Robert Arnold

Yeah, it was just an experiment. It actually turned a bit blue by morning. I run a airstone at night. And it was a lighter green (approaching greenish-yellow) tonight when I got home from work. I have distilled water now so I'll fix that tonight.These "drop checkers" are a cool concept and I appreciate everyone's efforts on this thread.


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## hooha

How often do you have to change the indicator solution? Is there any advantage using a different buffering solution over baking soda?


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## hoppycalif

I am in a phase where I am neglecting my aquarium now - too busy with other things for now. So, I have noticed that the indicator solution gets dimmer in color over time, but still reaches the same color as it originally reached for the same bubble rate. My best guess now is that two weeks is about as long as I would let it go if I wanted accuracy. As far as the KH solutions goes, sodium bicarbonate works very well, is very cheap, and is widely available, so I don't see any advantage to trying anything else. The only things that would work would be carbonates or bicarbonates.


----------



## Gatorguy

I still have my original batch in the drop checker. It has been in there for about 2 months now. I can glance in the aquarium and see the solution. If the solution looks blue, I know I'm out of CO2 (which has happened a couple of times). If the solution looks kinda clear (with the lights and background, etc., it looks clear), I know I have CO2 in the water.

When I do my weekly water changes, the water level falls below the drop checker. By the time I am filling my tank up again, the solution is bluish looking. It turns clear by the end of the day.


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## hoppycalif

The color on mine stays correct, but seems to fade a bit. It is so cheap to recharge it I just do it about every two weeks.


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## hooha

Do you mix up a "fresh" batch of buffer solution every change? Or can I mix up 100ml at a time and store it for a while?


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## Naja002

A DIY HOB Drop Checker and pH Controller from Sept. '92:

The Krib



> The only upkeep is to replace the water sample and reagent at water changes.


HTH


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## hoppycalif

Naja002 said:


> A DIY HOB Drop Checker and pH Controller from Sept. '92:
> 
> The Krib
> 
> HTH


Don't be misled by that article. You can't hang this on the back and have part of it outside of the tank and part inside. If you try that you will get a difference in temperature between the tank water and the drop checker water, which will cause slow distillation of the warmer water to transfer water to the cooler water, changing the KH of the reference water. Also, it doesn't work with tank water in place of KH reference water, and it reacts so slowly to changing tank water conditions that it is useless as a pH controller or a CO2 controller.

If you make up a bottle of KH reference water, and seal it tightly, it should be good for several months at least. Since the indicator solution is a dye it can't be completely stable, so if you add the indicator solution to a bottle of reference KH solution, at least do it in a small bottle, and store it out of direct light. Don't forget that some plastic bottles allow water vapor to leave the bottle very slowly, which would change the KH of the water. (Store a plastic bottle of water for a couple of years and it starts to collapse.)


----------



## u2_crazy

This has been a very good thread, long however.

Anywya, I consider myslef pretty new to the CO2 injection and am at a point where I have to decide where to go with CO2.

Some questions I have about this CO2 dropper is:
1. The red sea model looks nice and appears to be pretty cheap, is it recommended for those that aren't creative enought or have the time to DIY?

2. The KH and the Distilled water, how do you test it? I have a test strip kit but not a liquid test kit for KH. If I mix a mason jar worth, would the water last?

3. how often do you need to refill the dropper?

4. If I go with the red sea, once the reagent runs out, can I use normal PH reaent from my AP test kit? do you use the high range or low range ph indicator?


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## Naja002

Hi Hoppy,

Glad You realize these things straight-away. I didn't put much time or thought into the article--just thought I would share it and see if it had any value. Thought that it might have been a "Lost Technology" :spy: I got the link from a recent thread here at APC.....


:faint:


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## hoppycalif

u2_crazy said:


> This has been a very good thread, long however.
> 
> Anywya, I consider myslef pretty new to the CO2 injection and am at a point where I have to decide where to go with CO2.
> 
> Some questions I have about this CO2 dropper is:
> 1. The red sea model looks nice and appears to be pretty cheap, is it recommended for those that aren't creative enought or have the time to DIY?
> 
> 2. The KH and the Distilled water, how do you test it? I have a test strip kit but not a liquid test kit for KH. If I mix a mason jar worth, would the water last?
> 
> 3. how often do you need to refill the dropper?
> 
> 4. If I go with the red sea, once the reagent runs out, can I use normal PH reaent from my AP test kit? do you use the high range or low range ph indicator?


The Red Sea model will work as well as any of them. The principle this works on is so simple even crude DIY units work fine. In my opinion the only advantage of the glass ones is that they look nice in the tank.

You can mix the KH solution without a test kit, but then you need a digital balance that will measure accurate to +/- .01 grams, and a volumetric flask that will measure at least a liter of water accurately. If you mix 4.99 grams of bicarbonate of soda that you have baked at low heat for several minutes to dry it out, with 5 liters of distilled or DI water, you will have 5 liters of 40 dKH water. Then mix 10 ml of that with 90 ml of distilled or DI water, and you will have 100 ml of 4 DKH water. This should be more accurate than depending on a test kit, and you can store both the 40 dKH and the 4 dKH solutions in airtight bottles for an indefinite time.

You can use the reagent from any pH test kit, if the kit gives yellow at about pH=6 and blue at about pH=7.2.

The solution in the drop checker will last at least two weeks, with no problems. But, eventually you will need to clean off the "biofilm" on the drop checker, and add fresh solution to it.


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## claire09876

Hello,
I'm very new to all this. I'm not sure what you mean by distilled water for your drop checker and why that's important. Could you explain please? I'm assuming from your discussion that you can change the KH of this by adding bicarb of soda. KH is the water hardness right?! So it will be very different depending where you live in the counrty (I'm in the UK).

Sorry new to website and didn't realise there was more after 1st page!!!! Maybe there are answers in the other 19 pages!!!! Sorry if I have interupted your discussion on something else.....can I delete an entry and how?

Thanks
Claire


----------



## Squawkbert

claire09876 said:


> Hello,
> I'm very new to all this. I'm not sure what you mean by distilled water for your drop checker and why that's important. Could you explain please? I'm assuming from your discussion that you can change the KH of this by adding bicarb of soda. KH is the water hardness right?! So it will be very different depending where you live in the counrty (I'm in the UK).
> 
> Sorry new to website and didn't realise there was more after 1st page!!!! Maybe there are answers in the other 19 pages!!!! Sorry if I have interupted your discussion on something else.....can I delete an entry and how?
> 
> Thanks
> Claire


You use distilled water to make your 4dKH solution. If you use plain water, pH could be off as a result of something other than the bicarbonate.

PS - for you "real chemists" 4dKH corresponds to 0.06648mM Na Bicarbonate (if my math is right).


----------



## hoppycalif

*NEW: Membrane style DIY Drop Checker*

I have a workable, DIY, easy to make design now for a membrane version of the drop checker. Tomorrow I will make a couple to do some more testing. Here is the sketch:









This design will allow you to reduce the thickness of the KH water solution to as thin as you can use and still see color differences, thus making it react rapidly. It also will seal well, so leakage of the solution will not be a problem. And, you can use either Tyvek or Cole Parmer membrane, or just about any other membrane on it. Installing the membrane will be as easy as I can make it be. All of the materials are readily available from a Tap Plastic store (clear acrylic tubing) and a hardware store (for O-rings), plus a 1/2" diameter probe holder/vacuum cup from the LFS. I feel good about this one!!

This is a result of a lot of experimenting I did and reported on the Barr Report, see: Gas Permeable Membrane Drop Checker - Barr Report

To explain this some more, the top O-Ring is to seal the drop checker fluid in the chamber (the blue green color on the sketch), and the bottom O-ring is just like a rubber band to hold the membrane on the device. I know from testing that if the thickness of the fluid layer is only around 1/16 inch this will react in less than an hour, probably less than 30 minutes. I haven't tried to make the checker solution strongly colored enough to go below 1/16 inch thickness, but it would be worth trying it thinner, to see if a 5 minute response time is achievable. I expect to be able to make one of these in less than 30 minutes with hand tools.


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## Squawkbert

Nice - I've been playing w/ some different membranes that are more commonly available (no luck yet).

Please post some part numbers or specs for the membranes you've got working!


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## hoppycalif

Cole Parmer YSI 5775 "Oxygen Probe Service Kit" is what I used, and I just noticed that this is made by YSI Incorporated of Yellow Springs, Ohio. 
Ordindary Tyvek, a building wrap material is the other usable material I have tried. Both work for me, and both have their own advantages and problems. The Cole Parmer material is essentially invisible. It is a very thin, completely transparent membrane that you can see if you get light reflecting off of it just right, but otherwise it isn't visible. So, it is hard to work with easily. And, for me it didn't work any better than Tyvek. But, Tyvek is white, so you can't see through it, and it is a coarse material that likely has varying properties depending on where on the sheet you cut out a piece. Tyvek is sold in big rolls of 8 foot wide material - more than you could possibly want if you aren't building a house.
I tried Goretex "vents", which are a dark gray, adhesive backed membrane, made for venting electronic boxes. All I have of those are 1/2" diameter ones, which have a 1/4" diameter area in the middle with no adhesive on them. They work too, but the adhesive didn't stick well to acrylic for me, and I suspect they allow some water to go through the membrane. That material in a larger size would probably work, except the color and opaqueness make it hard to see the solution color changes accurately. 

Once I make a couple of the devices I sketched above I plan to do some more side by side testing, including leaving one in the tank for several days to see how long the membrane will be effective before biofilm plugs it up.


----------



## Squawkbert

I wonder if some used clean-room type garment scraps would work, they're made of Tyvek but there's enough of a texture to them that sealing could be an issue...


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## hoppycalif

Squawkbert said:


> I wonder if some used clean-room type garment scraps would work, they're made of Tyvek but there's enough of a texture to them that sealing could be an issue...


Regular building Tyvek has a texture too, but holding it tight to an O-ring makes it seal well. If you have some of those scraps to spare, PM me. I would love to try them out. I am inclined to think that a white opaque material like Tyvek will end up being the best DIY device material we can get.

Another question: if garments are made of that stuff, it must be possible to buy the garment grade material itself. Do you know where to do that?


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## hoppycalif

Just to update my progress on membrane style drop checkers:
Big problems! Once you reduce the quantity of fluid in the device down to where I have it now - a disk about 1/2" dia by 1/32 inch thick - it becomes almost impossible to load the fluid into it. Surface tension effects, wicking, and just unsteady hands make it very hard to seal up the fluid without losing it all. I finally managed to get one set up with the Cole Parmer membrane by freezing the fluid in the device before trying to put the cover membrane over it. That worked. And, the reaction time for the device was just about 5 minutes or so. But, the problem with loading it makes me think this is a dead end.

Next idea: Place a disk of acid free, non-buffered white blotting paper in the device, and soak that with the fluid. That will immobilize the fluid so the covering membrane can be added. If I can find some acid free, non-buffered paper I will try that today.


----------



## junco

Quick question... do you have to use the same amount of pH indicator that the test kit suggests? For example, if I'm supposed to add 7 drops of the indicator solution to 5 ml of water... do I need to do the same for my drop checker? I only ask because I made mine very small. I don't think all that liquid will fit in it.


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## hoppycalif

I have experimented with adding double and triple doses of indicator reagent to a pH test tube, to see if the color is any different. All that happened was that the color become more intense. Eventually the color gets murky and hard to "read" - that would be too much indicator reagent. In drop checkers I have been using from 2X to 4X doses of indicator. Intuition tells me that it is possible to use too much indicator reagent, but I suspect that would be more than 10% of the total volume of solution.


----------



## junco

well that's great. man i'm stupid. i just checked and my drop checker can hold a total of 2.5 ml of liquid. so what do I do, use a half dosage of indicator solution? that won't even work though... if i put 2.5 ml of water in it, the indicator solution would make it overflow. i guess i'll have to do 2 ml of water + 3 drops of solution or so. would that work?


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## redstrat

I use 2-4 drops per 1ml water


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## hoppycalif

hoppycalif said:


> Just to update my progress on membrane style drop checkers:
> Big problems! Once you reduce the quantity of fluid in the device down to where I have it now - a disk about 1/2" dia by 1/32 inch thick - it becomes almost impossible to load the fluid into it. Surface tension effects, wicking, and just unsteady hands make it very hard to seal up the fluid without losing it all. I finally managed to get one set up with the Cole Parmer membrane by freezing the fluid in the device before trying to put the cover membrane over it. That worked. And, the reaction time for the device was just about 5 minutes or so. But, the problem with loading it makes me think this is a dead end.
> 
> Next idea: Place a disk of acid free, non-buffered white blotting paper in the device, and soak that with the fluid. That will immobilize the fluid so the covering membrane can be added. If I can find some acid free, non-buffered paper I will try that today.


Update: The paper didn't work at all. Paper just doesn't absorb enough fluid to become colored enough to work. But, I tried a sponge and that was a different story. I bought a pack of those little sponge wedges that women use to apply or remove make up. Then sliced a thin piece off of one, about 1/16" thick or less. Cut it into a round disk. Used a 1/2" acrylic tube, about a half inch long as a holder. Put the sponge on a piece of Tyvek, soaked it liberally with 5 dKH water and added two drops of indicator reagent. Then I laid a piece of Cole Parmer membrane (transparent) on top and attached this sandwich of membrane sponge membrane to the acrylic tube using an O-ring as a rubber band to hold it on and seal it off. Immediately put it into the tank. And, in about 5-10 minutes it was green like my glass drop checker. Easy to make, easy to load with fluid, and seems to work like a charm so far. I will play with it some more tomorrow and post a photo if it still looks good.

The Tyvek I used was a piece of a Priority Mail envelope, which is a thinner Tyvek than building wrap and a lot cheaper. I'm not sure if the CO2 passed thru both membranes or just one, so I don't know for sure that this Tyvek is as good at passing gas as building wrap is.


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## schaadrak

Quick thought. I might not explain this right, but here goes:

Why not cut a large sirynge in half, and put some of the solution in the bottom half (the half with the plunger). Then attach the membrane to the opening and push the plunger in until the fluid is against the membrane. If the membrane is gas permeable, it will let the air out of the chamber , leaving just the solution.

Did I say that right?


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## Squawkbert

The gas permeable nature of the membrane is not such as to allow the rapid forceful pushing of air through it (maybe if you made an evening of it...).

Re paper idea... Oh well, it was worth a try. As soon as I get the membrane, I'll make the mini-autosampler vial version and get a pic up here.

I suspect it will work out pretty well and I already have the 4dKh/Indicator solution prepared...

I'm thinking that 4dKh isn't enough for my 46g tank. I'd been running just 1 1/2 gal. yeast reactor w/ a pretty good diffusion system and it's been showing green. I added another (full gallon) reactor 2 days ago... no color change. The checker in my 5g stays green/borders on yellow, but it has its own 1L reactor w/ a good airstone right below the filter 'waterfall' output.


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## hoppycalif

schaadrak said:


> Quick thought. I might not explain this right, but here goes:
> 
> Why not cut a large sirynge in half, and put some of the solution in the bottom half (the half with the plunger). Then attach the membrane to the opening and push the plunger in until the fluid is against the membrane. If the membrane is gas permeable, it will let the air out of the chamber , leaving just the solution.
> 
> Did I say that right?


I understand what you are proposing. And, I think it would work, but it might take a few minutes to push the air out, plus you would have to be careful not to push hard enough to push the membrane off the end of the syringe. It would look clunky, but should work ok. If you try this, try to keep the amount of fluid small enough that the thickness of the fluid in the syringe is only a 1/16" or less. The thinner the layer of fluid, the faster it can respond. Another problem you would need to solve is how to see the fluid color. If you use tyvek you can't see thru it, so the only way you could see the color is thru the side of the syringe.


----------



## banderbe

I am using a drop checker from Hong Kong. I made 4 dKH water from RO/DI, put it in the drop checker along with six drops of AP pH test.

It was dark blue, and within a few hours was light green bordering on yellow. Great!

Well, the weird thing is that the drop checker water stays that color, even after a night of no CO2 and surface aeration with an air stone.

Seems pretty weird to me.. I would expect it to return to a blue color..


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## schaadrak

As soon as I posted that I thought to myself, "How the Heck are you supposed to see the solution through the plunger?"

Oh well, I did come up with another suggestion. You could assemble it while submerged in the solution. Meaning put the container in a larger container that is filled with the indicator and then attach the membrane.

And also I came across these while in my garage:









There little containers of paint that you can get just about anywhere. They're small, transparent, water tight (maybe) and cheap. What I figure I'd do is cut off the bottom and glue a piece of an Tyvek envelope to it. Then fill the container with indicator solution and snap the lid on and *BLAMMO!* instant DIY drop checker. When the indicator solution goes south, flip open the lid and change solutions. Simple, eh?

The only problem I can think of is water and/or solution wicking between the lid and the top of the container. If the container is full of water and I squeeze it hard enough (probably harder than any pressures it will actually endure while in the tank) a small amount of water seeps out at the hinge. I'm not sure if the gap is there because of warping and flexing of the sides from me squeezing it or not so I'm currently performing an experiment. I've filled the container with water and red food coloring and put it in a bowl of plain water. Over the course of the next few days, I'll check to see if the food coloring has leeched into the plain water.

Here is the container floating in the "Test Chamber":









It's cap side down so that the entire cap-to-container junction is completely submerged. If it passes, the next test is to put some indicator solution in the container and submerge it in a water and vinegar solution and observe if there are any changes over the course of a week.

I'll try to post every evening over the next week as to the progress.

Tschuss,

Kent


----------



## hoppycalif

banderbe said:


> I am using a drop checker from Hong Kong. I made 4 dKH water from RO/DI, put it in the drop checker along with six drops of AP pH test.
> 
> It was dark blue, and within a few hours was light green bordering on yellow. Great!
> 
> Well, the weird thing is that the drop checker water stays that color, even after a night of no CO2 and surface aeration with an air stone.
> 
> Seems pretty weird to me.. I would expect it to return to a blue color..


That does seem weird. I am finding that the CO2 level in the tank drops very slowly, but by morning my drop checkers all show blue or near blue. And, I don't use an air stone at night, or increase the surface agitation. How are you turning off the CO2 at night? Obviously, I am thinking that you aren't really shutting it off.


----------



## hoppycalif

schaadrak said:


> Oh well, I did come up with another suggestion. You could assemble it while submerged in the solution. Meaning put the container in a larger container that is filled with the indicator and then attach the membrane.
> 
> Tschuss,
> 
> Kent


Now that is a simple, embarassingly obvious, solution to my problems with trying to get a very small amount of solution in my membrane drop checkers. I fell into the trap of mixing only as much solution as I needed, rather than waste precious water. But, there is no good reason for not mixing a cupful at a time, and dumping what isn't needed - other than the waste of indicator reagent.

Are those paint containers art paints, from an art supply store? They are most likely polyethylene, which is virtually impossible to cement anything to. But, a hole in the cap, with a membrane liner, with the cap doing the sealing and retaining of the membrane might work well. Don't forget, to get fast response you need to minimize the thickness of the "disk" of solution. The time it takes to reach equilibrium is proportional to the volume of solution and inversely proportional to the area of membrane. So, maybe cutting off the bottom of one of those containers, keeping just the lid and a thin section of the body, with the membrane covering the missing bottom, retained by the lid?


----------



## banderbe

hoppycalif said:


> That does seem weird. I am finding that the CO2 level in the tank drops very slowly, but by morning my drop checkers all show blue or near blue. And, I don't use an air stone at night, or increase the surface agitation. How are you turning off the CO2 at night? Obviously, I am thinking that you aren't really shutting it off.


A timer turns off a solenoid.. and I use a Red Sea 500 reactor so it's pretty obvious when CO2 is being injected because a bubble will form. There's that and the fact that the bubble counter attached to the canister doesn't show any bubbles 

I guess it doesn't matter.. it just makes me a little suspicious of what the green color is really telling me..

I think I am going to try using the drop checker in a glass of tank water at equilibrium with the room.

I expect it should stay blue..


----------



## hoppycalif

Schaadrak's idea for how to load one of these things inspired me to try a new, even simpler design, but one which relies on an O-ring to seal the membrane where it is smooth, instead of trying to seal it by pressing the folds of the membrane to the plastic body of the device using a rubber band. This is what I came up with:
















Once all of the acrylic cement, and the white nail polish dries well I will try loadiing it with Schaadrak's method, and sticking it in the aquarium.

But, I will have to make some more 5 dKH distilled water first - put on my Chemist's lab coat, with the pocket protector, etc.


----------



## banderbe

You know, I am wondering about something here.. the idea as I understand it is that the liquid inside the drop checker contains no acids and then after it is put in the tank, exchanges CO2 in the air pocket with the water from the tank until they are at equilibrium.

Fine, that makes sense.. but why won't other acids in addition to carbonic acid also enter the water in the drop checker?

I think the point of the drop checker was to isolate carbonic acid from other possible 'contaminating' acids in the tank water that render the usual KH/PH/Co2 calculation erroneous.

It seems like if there was say, tannic acid from driftwood that it too would enter the water in the drop checker.. 

I'm sure this has been covered.. so help me understand why we are so positive that CO2 is the only thing that can enter the water in the drop checker.


----------



## hoppycalif

banderbe said:


> You know, I am wondering about something here.. the idea as I understand it is that the liquid inside the drop checker contains no acids and then after it is put in the tank, exchanges CO2 in the air pocket with the water from the tank until they are at equilibrium.
> 
> Fine, that makes sense.. but why won't other acids in addition to carbonic acid also enter the water in the drop checker?
> 
> I think the point of the drop checker was to isolate carbonic acid from other possible 'contaminating' acids in the tank water that render the usual KH/PH/Co2 calculation erroneous.
> 
> It seems like if there was say, tannic acid from driftwood that it too would enter the water in the drop checker..
> 
> I'm sure this has been covered.. so help me understand why we are so positive that CO2 is the only thing that can enter the water in the drop checker.


The membrane is supposed to be gas permeable, but not liquid permeable. So, liquids can't pass thru it. And, as long as any gas on both sides is in equilibrium across the membrane, no net exchange of gases will occur either. So, if there is tannic acid on one side, but not the other side, the acid will be a liquid, which cannot pass thru the membrane. But dissolved gases are not liquid, so they do pass thru. I'm not yet clear on whether O2 and N in solution in the tank will pass thru the membrane but they should.

I found that if you just leave the membrane drop checker out in the air water vapor will pass thru it from the water inside to the low humidity outside, until the water is all gone. But, the indicator solution and the sodium bicarbonate seem to remain in the drop checker, leaving a very blue liquid there.

If you were to put a hot drop checker in cold water there would be water vapor passing from the drop checker to the tank, until the temperatures equalized. That would be from the higher vapor pressure inside the device than the tank water.


----------



## schaadrak

banderbe- The way that I understand it, gas molecules in general are do not have the cohesive properties that liquid molecules do, so they are able to pass through the small holes of the membrane. Plus I think tannin molecules are just plain old too big.

Hoppy- I'll start testing to see what kind of attachment method works best. I don't think anything could fit in that between that lid and still shut properly

Also paint container update; its been almost twenty-four hours with no sign of leaking or wicking of the red dye. Things are looking good.


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## blyxa

hoppy, I don't quite understand how you make your new design?


Thanks


----------



## blyxa

*Cole Parmer*

How would you get a membrane from Cole Parmer? Now, I understand the device however couldn't you make the tube smaller? What about a natural latex glove? It is like a balloon and deflates when filled with air but it doesn't leak.


----------



## hoppycalif

blyxa, the basic idea for a membrane type drop checker is to use the membrane to allow CO2 in the water to equalize with the CO2 in the drop checker, and detect the amount of CO2 by watching the change of color of a pH indicator solution mixed with the drop checker water. The only advantage I see for doing it this way is to get a drop checker that reacts much quicker to changing CO2 concentration than does the regular air gap drop checker.

The reaction time for a membrane type drop checker is proportional to the volume of fluid in it that has to dissolve CO2, and inversely proportional to the area of membrane that allows the CO2 to enter the drop checker fluid. To minimize the reaction time requires maximizing the membrane area, while minimizing the volume of fluid. If the fluid is in the form of a round disc, like a coin, for example, the volume is the round cross section area times the thickness. If there is a membrane on one side of that disc, the area is pi times the diameter of the disc squared. So, the reaction time is proportional to the volume of fluid divided by the membrane area, or pi times the diameter squared times the thickness divided by pi times the diameter squared. That reduces to just the thickness. So, minimum reaction time requires minimum thickness of the fluid disc.

In order to see the color of the fluid disc the disc has to be thick enough to see the color - obviously a one mil thickness will never show a color, and a one inch thickness will show the color brilliantly. So, achieving a minimum reaction time conflicts with being able to see the color. One way to get around that is to view the color through the diameter of the disc instead of the thickness, but the mechanics of assembling the device, holding the device in the water, sealing the membrane, etc. make it very hard to keep a thin disc while still allowing for viewing the fluid thru the diameter.

A compromise is to make one side of the container very opaque white, so the color shows up better against the white background. This can be best done by using a Tyvek membrane for one side, and a transparent membrane for the other side - the viewing side. But, doing this only doubles the membrane area, cutting the reaction time in half. Since a big slug of fluid, like in the air gap drop checkers, takes a couple of hours to reach the final color, a reduction by half isn't very signiificant. We need a reduction by more than a tenth.

Another problem with using membranes, at least it's a problem for me, is sealing the membrane to keep the fluid inside.

All of the above led me to the simplest design - a 1/16 inch thick O-ring glued to a plastic plate, to make a recess for the fluid, with a membrane draped over that, so the O-ring seals against the membrane to hold the fluid in. The mechanical problem of attaching the membrane can be solved by making the plastic plate be a solid plastic cylinder, the same diameter as the outside diameter of the O-ring. Then the membrane can be held in place with a rubber band around it where it drapes over the plastic cylinder, and another O-ring makes a great rubber band. In order to hold this device in the aquarium I chose to glue an air line holder suction cup to the side of the plastic cylinder, which meant the cylinder had to be about 1/2 to 1 inch long.

To make the back face of the fluid disc white while still using clear acrylic for the plastic cylinder, I used white nail polish on the end of the cylinder. It took about 4 coats to get an opaque white coating, and I used the last coat as glue to attach the O-ring to the plastic cylinder. (Nail polish is acrylic glue with coloring in it.) Now, since I didn't have any solid plastic rod, other than a 3/8 inch diameter, for which I didn't have an O-ring to fit, I used a piece of 5/8 inch acrylic tube, with a 1/2 inch acrylic disc glued in the end, in place of the solid plastic rod. (I used the parts I had on hand.)

How do you get Cole Parmer membrane? Go to:YSI Meter Accessories And Replacement Membrane Kits - Cole-Parmer Catalog
The membrane kit costs about $30 with shipping included, and you get about 20-30 membranes, good for at least that many drop checkers. Each membrane is about 1.5 inch by 4 inch.

Natural latex is a gas permeable membrane, as I recall. So, a natural latex glove finger could be used to make a membrane type drop checker. All that is required is the engineering to figure out how to hold it together, seal the fluid inside, be able to see the fluid inside, with a white background, and hold it in the aquarium. The design possibilities for membrane drop checkers are almost endless.


----------



## banderbe

I wasn't asking about the membrane. I was asking about the basic drop checker.

What assurance is there that only CO2 will enter the colored water in the drop checker?

If CO2 can enter, then other acids might be able to as well.



hoppycalif said:


> The membrane is supposed to be gas permeable, but not liquid permeable. So, liquids can't pass thru it.


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## banderbe

In other news, I removed the drop checker from my tank and stuck it on my mirror in my bathroom. Within a day the color went back to blue.

I had also taken a glass full of water from the aquarium and left it out over night to degass.

I submersed the drop checker (now blue) into the glass of water, and it is staying blue, confirming that indeed the CO2 level in the glass of water went way down.

So I guess I still have no idea why on Earth the drop checker's color stays green even after a night of surface aeration and no CO2.

Weird. But, I am comfortable in believing that green means good CO2 IF it is true that ONLY CO2 can enter the drop checker's water.

I still wonder why other acids in the tank water can't also enter a gas phase and enter the drop checker's water.

Hoppy, can you confirm for me the intent of the drop checker? 

In a tank with a giant piece of drift wood, e.g. tons of tannic acid, your drop checker (not the membrane idea) should still give an accurate reading of CO2. Is that correct? 

So there is the unstated assumption here that acids other than CO2 cannot pass through the gas pocket inside the drop checker.

I still want to know how we know that...


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## hoppycalif

banderbe said:


> In other news, I removed the drop checker from my tank and stuck it on my mirror in my bathroom. Within a day the color went back to blue.
> 
> I had also taken a glass full of water from the aquarium and left it out over night to degass.
> 
> I submersed the drop checker (now blue) into the glass of water, and it is staying blue, confirming that indeed the CO2 level in the glass of water went way down.
> 
> So I guess I still have no idea why on Earth the drop checker's color stays green even after a night of surface aeration and no CO2.
> 
> Weird. But, I am comfortable in believing that green means good CO2 IF it is true that ONLY CO2 can enter the drop checker's water.
> 
> I still wonder why other acids in the tank water can't also enter a gas phase and enter the drop checker's water.
> 
> Hoppy, can you confirm for me the intent of the drop checker?
> 
> In a tank with a giant piece of drift wood, e.g. tons of tannic acid, your drop checker (not the membrane idea) should still give an accurate reading of CO2. Is that correct?
> 
> So there is the unstated assumption here that acids other than CO2 cannot pass through the gas pocket inside the drop checker.
> 
> I still want to know how we know that...


We know it because there will be no distillation occurring unless the drop checker water and the tank water are at different temperatures. Acids are just water with ions in it, with more H+ ions than OH- ions. If the acidic water becomes a gas it has to be H2O molecules, not a mix of ions and molecules. Even if there were distillation, the distillate would be pure water with no ionic solutes. That's why distillation gives us water without any salts in it.

So, only gas can go across the air gap from one glob of water to the other. Oxygen, nitrogen, CO2 and any trace gases will also go across. Volatile organics such as alcohol will also go across the gap. But acids and bases won't, since by definition, they are ions, not molecules.

That is how I see it anyway. I'm a bit troubled by knowing I can smell muriatic acid, which certainly appears to mean the vapors I smell are gases and acid. Perhaps someone with a lot more chemical knowledge than I have would like to discuss this?


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## schaadrak

When you smell acids you are indeed smelling the acid that has evaporated into a gas. This means that there is a possiblity that some acids could cross the air gap and end up in the indicator solution, but that pecentage is probably too small to affect the results of what we're testing for, since the surface area in the air gap is small and the air gap is saturated with evaporated water. The membrane would not allow acids in gaseous form through since evaporation only occurs at the surface.

I think that's right.


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## Squawkbert

*2 things*

Regular drop checkers staying green - maybe (I'm speculating here) there isn't enough water movement around it, or it's too close to the outlet of the CO2... if CO2 actually displaces air in the checker instead of equilibrating with it, you won't get it back out unless you remove the drop checker so that regular air is mixed in again (CO2 is heavier than air and could blanket the surface of the checker, but I would think it would go yellow if this happened).

Also - it isn't faster (or slower) than the open types, but it won't leak, even if flipped... and it's super easy to assemble (2mL LC sample vial, some of Hoppy's probe membrane, 4dKH purified DI, API pH indicator solution):









The red thing is the setting knob from my Visitherm Stealth heater. It's a tight fit, but that's a christmas mini-light suction cup holding the checker to the inside wall of my 46 (also w/ new pic today - see sig. link)


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## schaadrak

Squawkbert said:


> Regular drop checkers staying green - maybe (I'm speculating here) there isn't enough water movement around it, or it's too close to the outlet of the CO2... if CO2 actually displaces air in the checker instead of equilibrating with it, you won't get it back out unless you remove the drop checker so that regular air is mixed in again (CO2 is heavier than air and could blanket the surface of the checker, but I would think it would go yellow if this happened).
> 
> Also - it isn't faster (or slower) than the open types, but it won't leak, even if flipped... and it's super easy to assemble (2mL LC sample vial, some of Hoppy's probe membrane, 4dKH purified DI, API pH indicator solution):
> 
> 
> 
> 
> 
> 
> 
> 
> 
> The red thing is the setting knob from my Visitherm Stealth heater. It's a tight fit, but that's a christmas mini-light suction cup holding the checker to the inside wall of my 46 (also w/ new pic today - see sig. link)


Where is the membrane located on that?

*Paint Container Update*- I can see a tinge of red in the water, so it looks like there is some wicking going on. Also that sample vial made me realize that my wife could get me something similar to those since she works in a DNA lab and they have to guard against cross contamination. I'll see if she can suggest anything that might be closer to the shape that Hoppy has.


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## Squawkbert

The membrane has replaced the PTFE/silicone rubber cap liner in the yellow cap (that has a big hole in it for instrument needles to pass through).

If your wife can bring you LC vials & some good water (high resistivity, polished, Milli-Q type) & you get some gas permeable membrane, you can make these things all day.


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## hoppycalif

We need to keep in mind that gas permeable membranes need to be cleaned periodically to eliminate the biofilm buildup. I understand that a bleach solution would do it. But, I'm not sure if any of the bleach would make its way into the indicator solution and spoil it. Also, if a fast reaction time is a goal, the thickness of the fluid behind the membrane has to be as thin as possible. A penny shaped slug of fluid is ideal, a "square" cylinder shaped slug isn't ideal. The perfect drop checker would have a slug of fluid only a few molecules thick sandwitched between two membranes, and would detect the pH electronically. That would be an almost instantaneously reacting device.


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## schaadrak

I have a idea for anyone who has an electric pH meter; make a long tube out of some membrane a little longer than your probe and only a smidge wider, seal up the bottom and fill the tube with some 4GH water. Then put your probe in and seal the top (somehow, I don't know if they have attachments that would work or if you would have to seal it with silicone or something). That would give you a large amount of membrane surface area and a small volume of "solution"


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## hoppycalif

*Another simple way to make membrane type drop checker*

I made another, almost foolproof membrane drop checker. It has a 1/16 inch thick layer of KH reference fluid, for rapid response, an O-ring to seal the membrane, and is easy loading.
































The blue fluid photo was when I first put both drop checkers in the tank. The green fluid photo is 1 1/2 hours later. So far I haven't checked on how fast the membrane one reacts. I had no trouble at all putting the fluid in it, with a couple of drops of pH reagent.

My next effort is one that I think will be easier to see the color on from outside the tank, and which can be used with either a tyvek or clear membrane. But, I haven't tried making it yet. (This is fun!!)

(Originally posted on the Barr Report.)


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## Squawkbert

That one is pretty easy to see. You should pull the ADA style one & yours above the water line, let both turn blue and see which turns green faster when returned to the tank.


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## hoppycalif

Squawkbert said:


> That one is pretty easy to see. You should pull the ADA style one & yours above the water line, let both turn blue and see which turns green faster when returned to the tank.


You can't leave either one of those out of water very long or water vapor escapes, raising the KH. I pulled the membrane one out when it was very green and put it in a glass of tap water. It took about 30 minutes to go to a blue green and about an hour to become virtually blue. Like any device of this type the color approachs the equilibrium color asymptotically, so to characterize the response time you need to time it to an intermediate color. Once it is thoroughly blue I will put it back in the tank and time it the other way.

Then I plan to put a tiny sponge in the fluid chamber to reduce the fluid volume and see how much that reduces the reaction time. I did this before on another one and it makes a significant differenct.


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## hoppycalif

The sponge helped the response time a bit, but not by as much as I expected. It took 10 - 15 minutes for the color to reach about 2/3 of the way to the final color. So, I tried one last design, using the Tyvek Priority Mail envelope material:

























This one used the same size KH reference sample, the same amount of indicator reagent, a sponge, but a Tyvek membrane. It reacted exactly the same as the one above using the Cole Parmer transparent membrane. This one is easy to make, a piece of plastic, an O-ring, and a suction cup airline holder. It took me about an hour to make. It is easy to load, easy to read, easy to make, and responds almost 10 times faster than the glass drop checker. And, everyone should be able to get a Priority Mail envelope to use as a membrane. I think I have exhausted all of the ways to make a drop checker!


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## caymandiver75

Wow nice job Hoppy! Should get a patent on that idea.


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## caymandiver75

*11 Feb 07*

Today I put distilled water with a KH of 5 in my Red Sea CO2 indicator but I'm having trouble deciding what my CO2 ppm is from it. Below is a photo that I just took. I can't decide if the ph in it is 6.6, 6.7, 6.8 or what.

Original


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## Jubs

hoppycalif said:


> The sponge helped the response time a bit, but not by as much as I expected. It took 10 - 15 minutes for the color to reach about 2/3 of the way to the final color. So, I tried one last design, using the Tyvek Priority Mail envelope material:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> This one used the same size KH reference sample, the same amount of indicator reagent, a sponge, but a Tyvek membrane. It reacted exactly the same as the one above using the Cole Parmer transparent membrane. This one is easy to make, a piece of plastic, an O-ring, and a suction cup airline holder. It took me about an hour to make. It is easy to load, easy to read, easy to make, and responds almost 10 times faster than the glass drop checker. And, everyone should be able to get a Priority Mail envelope to use as a membrane. I think I have exhausted all of the ways to make a drop checker!


I like this design as I have all the supplies to do this one but I can't figure out where the reading is coming from... Is it just the sandwiched Tyvek membrane spaced from the O ring that is allowing the exchange in reading ? Or am I missing something as to where membrane is exposed to the water ?


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## hoppycalif

Jubs said:


> I like this design as I have all the supplies to do this one but I can't figure out where the reading is coming from... Is it just the sandwiched Tyvek membrane spaced from the O ring that is allowing the exchange in reading ? Or am I missing something as to where membrane is exposed to the water ?


One flat piece of acrylic has a hole in it. The membrane goes across the hole, over the O-ring, and then between the two pieces of acrylic. That leaves a disc consisting of membrane, piece of sponge soaked with KH reference water, acrylic, with the O-ring sealing in the KH reference water. I wasn't too happy with this design, and I'm not all that sure the tyvek membrane doesn't leak a bit. Personally, I am giving up the quest for faster response, preferring the simplicity of not using the membrane.


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## Jubs

Thank you Hoppy I understand exactly what you are saying now. I might try something like this soon thanks for the great write up and trying different types!


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## Color Me Blue

Can I say WOW! This has been a very informative thread. This answered my drop checker questions. Thank you for taking the time and energy to share all this.


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## dirtmonkey

Hoppy Wrote:
> I'm not all that sure the tyvek membrane doesn't leak a bit

Tyvek is only a one way street when a liquid with surface tension (like water with no surfacants) is only on one side, and air on the other. It is ALWAYS permeable to water vapor. Only surface tension of the water resisting against the small pores in the polyester allows it to hold water- but not permanently. It is a two-way street for water and even much larger molecules when wet through. Its pore size is not regular, there are larger and smaller holes. I know from experience with sterile cultures that it can only be effective in keeping out viruses and even some bacteria when it is dry on both sides. Those are obviously much larger than organic acid molecules of all kinds. It worked for you temporarily, but I think the true semipermeable membranes with the right structure for the job would be the only long-term solution (pun intended).

But I agree with you now that the hassle doesn't sem to be worth the gain over the regular partial pressure gas exchange testers the thread started with... now off to make one for myself (yeah, when I get around to it... )


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## Zamboniman

Whipped this DIY Drop Checker together in about 5 minutes with stuff I already had. Doesn't look too bad in the aquarium, now we'll see how it works. I just put it in so the regent is still blue. It's the air type rather than the membrane type so it'll take a couple of hours.


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## Squawkbert

Nice job on the "3-jigger drop checker"


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## hoppycalif

Wow! What a neat and easy way to make one of these gadgets. The only suggestion I have is to keep the quantity of water in it to a minimum to speed up the reaction time.


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## Blacksunshine

lol. nice shotglass DC. 

If anyones interested, I will be making some # of DC's in the next week. If you wanna save yourself some time and hassle PM me.


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## Laith

Zamboniman said:


> Whipped this DIY Drop Checker together in about 5 minutes with stuff I already had. Doesn't look too bad in the aquarium, now we'll see how it works. I just put it in so the regent is still blue. It's the air type rather than the membrane type so it'll take a couple of hours.


Not bad! What a simple but effective idea. 

I assume that's silicone you used to put it all together?


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## Squawkbert

hoppycalif said:


> Wow! What a neat and easy way to make one of these gadgets. The only suggestion I have is to keep the quantity of water in it to a minimum to speed up the reaction time.


Hoppy - I suspect it (speed) may also be a function of surface area than of volume in the "air gap" checkers. I've got one (air-gap one) that holds <2mL of indicator solution but it's in a tall, thin shell vial. It reacts slower than the membrane one (inverted bottle w/ hole in cap) in the same tank.

Once, it went yellow so I pulled it and stuck it to the outside of my tank, it took 3 days to change back to green. My membrane one went from blue to green in 3-4 hours when I added it to my 5g tank.

I need to refill the one in my 46g tank as the 96W light has not been kind to the indicator dye. I think I'll mount it a lot lower in the tank when I refill it (maybe in some shade provided by the sword that's taking over).


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## Zamboniman

hoppycalif said:


> Wow! What a neat and easy way to make one of these gadgets. The only suggestion I have is to keep the quantity of water in it to a minimum to speed up the reaction time.


Yes I was thinking the same thing and ended up emptying some of it out and using just a few ml in the bottom. Turned nice and green in about 1 1/2 hours.


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## Zamboniman

Laith said:


> Not bad! What a simple but effective idea.
> 
> I assume that's silicone you used to put it all together?


Yup, just some silicone. Took less than 5 minutes to put together, then a couple of days waiting for the silicone to cure. I took quite a bit longer mixing up the 4 dkh solution and ensuring it was EXACTLY 4 dkh. The package said fully cures in 24 hours so I gave it 48. Seems to work great so far.


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## hoppycalif

The real breakthrough in that shot glass design is thinking outside the box, by noting that there is no good reason to keep the two parts concentric. That suggests getting two sizes of test tubes, cutting them shorter and glueing the small diameter one inside the large diameter one as you did. Even doing the non-concentric thing when making one from acrylic tubes would be much easier. One could also experiment by making the air chamber glass much bigger than the water chamber glass, to see if that speeds up the reaction. Now I think anyone can make one of these, even the all thumbs people.


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## Zamboniman

hoppycalif said:


> The real breakthrough in that shot glass design is thinking outside the box, by noting that there is no good reason to keep the two parts concentric. That suggests getting two sizes of test tubes, cutting them shorter and glueing the small diameter one inside the large diameter one as you did. Even doing the non-concentric thing when making one from acrylic tubes would be much easier. One could also experiment by making the air chamber glass much bigger than the water chamber glass, to see if that speeds up the reaction. Now I think anyone can make one of these, even the all thumbs people.


I agree about making the air chamber larger (in terms of horizontal area, not height) and the water chamber smaller to make the air/water interchange area as large as possible to hopefully speed up the reaction. My next one will be the same design but using an old test kit test tube inside one of the larger sized shot glasses. I could use an even larger sized glass of some kind but I don't want the thing too ridiculously large in my aquarium. It'll be interesting to time this and see if it improves reaction time.


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## Squawkbert

http://img479.imageshack.us/img479/5952/20070122fts5g3pz.jpg

^pic featuring a poorly designed air-gap DC - it's super slow to respond to change because of the ~3mm diameter at the top of a ~3cm column of indicator solution. Something along the lines of the shot glass design featuring a short, wide column of indicator solution should respond a lot faster (I feel another science fair project idea coming on).


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## billionzz

I have an ADA knock off drop checker and a Red Sea drop checker.
Plus I have made about 10 others with different designs.

The test tube drop checkers work but they are slow to respond. You don't even have to
attach the bottom test tube it will just float in place (see picture below).

When I first started using a drop checker I made one big enough to pull out and measure 
the 4 dKH water with my pH meter. It wasn't something I wanted in my tank forever, I just 
did it so I would feel confident that the pH indicator solution was correct. Here's a link showing 
how I put it together, you might be able to attach the shot glasses together like this so they 
would be straight.
http://www.plantedtank.net/forums/g...70-co2-measurement-checking-drop-checker.html

Bill


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## freydo

after having read this thread a few times, i'm going to be making a drop checker myself, probably starting off with something similar to billionzz's idea.

but all i have to say is, i didn't realize how little baking soda is needed to make a kH solution. since i don't have any sort of scale to use, it's pretty hard. instead i'm using a trimmed off/flattened wooden toothpick, i've pretty well gotten the measurements worked out to get 4-5dkH.

starting off with .25 tsp of baking soda to 1 ounce water, pretty well have me liquid rock, and blue fingers... don't ask


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## MTechnik

Sorry, been gone for a while. Trying to get my big tank back in order. Found this idea yesterday. Made one today. Went with the Shot Glass and Test Tube method.










Thanks for the awesome idea! Off to watch Borat and see if it changes color. I know there's more liquid than needs to be in there... but it's there now, it'll just take a smidge longer.

-MT


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## k-maub

I'm sure I'm missing something obvious, but as I understand it, atmospheric CO2 concentration is somewhere north of 300 ppm. Why then are drop checkers supposed to be blue when they are sitting out, and not yellow?

I say "supposed" because I think I "broke" mine when I tried adding pH drops to intensify the color, and after a few days it assumed a yellow color that has stuck, whether in or out of the tank.

I wish I paid more attention in chemistry.


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## banderbe

k-maub said:


> I'm sure I'm missing something obvious, but as I understand it, atmospheric CO2 concentration is somewhere north of 300 ppm. Why then are drop checkers supposed to be blue when they are sitting out, and not yellow?
> 
> I say "supposed" because I think I "broke" mine when I tried adding pH drops to intensify the color, and after a few days it assumed a yellow color that has stuck, whether in or out of the tank.
> 
> I wish I paid more attention in chemistry.


No, there's only about 3 ppm of CO2 in the atmosphere.

It should definitely be blue if it's exposed to the air for an hour or so.


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## Squawkbert

My reading indicates that there's ~300ppm atmospheric CO2, ~3ppm of which is willing to dissolve into aquarium water. In streams, lakes etc, you get more than 3ppm CO2 in solution (underground, minerals, other organisms contribute to CO2 more in nature than in aquariums).

Note to MTechnik - I bet that checker didn't change color ove the course of Borat - the test tube appears to be too skinny. I'd suggest a fatter one and a lot less liquid in it (enough to get liquid column height=width should be good).


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## banderbe

Squawkbert said:


> My reading indicates that there's ~300ppm atmospheric CO2, ~3ppm of which is willing to dissolve into aquarium water. In streams, lakes etc, you get more than 3ppm CO2 in solution (underground, minerals, other organisms contribute to CO2 more in nature than in aquariums).
> 
> Note to MTechnik - I bet that checker didn't change color ove the course of Borat - the test tube appears to be too skinny. I'd suggest a fatter one and a lot less liquid in it (enough to get liquid column height=width should be good).


Where do you get that information?

I thought a liquid would always reach equilibrium with its surrounding atmosphere.. so there should be the same amount in a standing body of water as there is in the surrounding air, up to the point of saturation of the liquid of course.

I would love to know why CO2 magically stays out of equilibrium.


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## dennis

The information is everywhere. Atmospheric CO2 levels are ~350ppm or .03% of the total volume of the atmosphere. I'll stop now lest another thread becomes locked

As for why drop checkers don't show atmospheric levels... A great many google searches, chemistry books and teachers, etc will all explain that the reaction between CO2 and H2O it is a complicated and intricate, multi-step process, compounded when one has extra ions already present in the water. CO2 is actually very soluable in water, about 1.45g/L at 25 degrees C. This means that water is capable of holding, in theory, 1450ppm CO2. This would never happen though as solubility and readiness to dissolute are two very different things. Because CO2 dissolves into water about 10,000 times slower than into air, the equilibrium with pure water is only 0.5-5mg/l depending on temp, pressure and water chemistry. This is fortunate because otherwise, all the water in the world would have a pH of like 2 or something.

The reason your drop checkers turn blue very quickly once out of the water is two fold. First, when the checker is in the water, any CO2 that makes it into the drop checker will find its way into the drop checker water because of pressure and equilibrium. For example, if you have 30mg/l CO2 in your water, the water in the drop checker, since it is in a sealed system with the aquarium, will very quickly reach equilibrium due to a difference in partial pressures between the two waters. If the CO2 in the aquarium lowers, or if you remove the checker from the tank and expose it to air, the pressure/concentration of the CO2 in the checker is suddenly higher than its surroundings and the CO2 exits, causing the color to switch back to blue. This process is hastened by the extreemly small volume in the drop checker and by the chemical fact that the CO2<=>H2O equilibrium is very low even though the solubility is high.

The term _equilibrium_ is a very confounding word actually. In almost all chemical reactions and processes, the concentrations of reactants and products is generally very squewed, even though the reaction is at equilibrium. A great many chemical reactions have equilibrium points at which the concentration of the products may be thousands or millions (sometimes even more) less that the concentration of what you started with. For example, if you look at the equilibrium point where H2CO3 and HCO3 are at equilibrium for one part of the CO2+H2) process, a concentration of H2CO3 in the water of 0.033M (hypothetical fully saturated level of the gas in water) the concentration of HCO3, at equilibrium, will be only 1.2x10^-6M!!!! Equilibrium doe snot mean the same.

Sorry for the lengthy post.


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## MTechnik

I replaced the velcro with fishing line and removed a lot of the reagent. I also added a piece of white solo cup clipped to the outside of the test tube, so that I have a white background for reading it.

You are very right - it wasn't green after Borat. Turns out I wasn't doing my CO2 dosing right, and now it's all fixed. This was just what the doctor ordered. Things have begun greening nicely, and soon I'll be able to trim away all the BBA covered growth.

-MT


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## k-maub

Interesting. So Dennis, is the implication that the small amount of air in the drop checker has an extremely high level of CO2 (if this scales linearly, something on the order of 3,000 ppm CO2), in order to maintain equilibrium?

Thank you for your explanation.


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## dennis

No. The air and solution in the drop checker, when its in the aquarium, has the same amount of CO2 as the aquarium water. In this case, the high equilibrium (high amount of CO2 in drop checker) is the result of the CO2 gas having no where to go but the water in the drop checker. In this case, if the pressure of CO2 in the aquarium water (called partial pressure and in this case is the same as concentration)) is higher than the pressure of CO2 in the drop checker, the concentration gradient will force CO2 out of the aquarium water in to the air gap and into the drop checker solution. It has to go there. The direction of change reverses as the CO2 in the aquarium drops and the drop checker has more CO2 than the aquarium... the CO2 will have a higher pressure/concentration in the check and will move to the aquarium. In this case, equilibrium is equal and it has no physical or chemical choice but to be as the two liquids are essentially in a closed system. Imagine pinching a balloon in the middle then inflating it so only half inflate... let the pinched part go and the whole balloon inflates. The balloon itself is the system and the air you push in must fill the whole thing.

If you take the drop checker out of the tank and put it in the air, even though the concentration of CO2 is higher in the atmosphere than in the checker, the CO2 will exit to the atmosphere anyway because there is nothing forcing a high equilibrium level. Its like opening the end of an inflated balloon so it flies around the room. True, pressure is involved more with the balloon, but the analogy should make it easier to understand. In the aquarium, CO2 goes into the drop checker because it has to go somewhere...in the atmosphere, CO2 leaves (or does not enter) because there are easier places for it to go.

Make sense?


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## k-maub

Hm. I see where you are going with that, but I don't see how the drop checker solution's interface has any "knowledge" of the condition outside of the drop cheker. That is, if the concentration of the air at the solution/air interface is 300 ppm, it should not matter what is going on at the exit of the drop checker. It is the relative values of CO2 in the solution and air that will dictate how much CO2 is diffused, I would think.

If 300 ppm CO2 in the atmosphere is only capable of raising water's CO2 ppm to 3, it is hard to believe that, even in a "closed system", air with ten times less CO2 (30 ppm) could possibly raise the drop checker solution to ten times more (30 ppm) that it would otherwise.

If CO2 is that much more easily dissolved in air than water, then by my reasoning, the 30 ppm water would reach equilibrium with 3,000 ppm CO2 air in the drop checker. Being ten times higher than atmosphere, this will bring the drop checker solution 10x higher than atmosphere, from 3 ppm to 30 ppm. Otherwise, if 30 ppm air can raise water to 30 ppm CO2, a sealed bag of half water/half air would eventually reach 300 ppm CO2 in the water (or 150 ppm or so once you subtract from the air's supply of CO2), possibly causing distress to fish being brought home from the fish store.

Am I making any sense?


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## epicfish

I enjoyed dennis' explanation, but I think it lacked a discussion of partial pressures, although he alluded to it with the phrase "nothing forcing a high equilibrium level".

Here's a list of terms and concepts I'll use to try to explain this...I don't want to clutter the text with this, so everything will be listed first.

http://en.wikipedia.org/wiki/Partial_pressure


> *Gases will dissolve in liquids to an extent that is determined by the equilibrium between the undissolved gas and the gas that has dissolved in the liquid *(called the solvent).





> The form of the equilibrium constant shows that the *concentration of a solute gas in a solution is directly proportional to the partial pressure of that gas above the solution*.


http://en.wikipedia.org/wiki/Co2


> It is present in the Earth's atmosphere at a low concentration of *approximately 0.04% *and is an important greenhouse gas.


http://en.wikipedia.org/wiki/Atmospheric_pressure


> In 1982, the International Union of Pure and Applied Chemistry (IUPAC) recommended that for the purposes of specifying the physical properties of substances, *"the standard pressure" *should be defined as precisely 100 kPa (≈750.062 torr) or *29.9230 inHg*


http://www.google.com/search?hl=en&q=29.9230+inches+to+mm


> 29.9230 inches = *760.0442 millimeters*


http://www.madsci.org/posts/archives/2001-09/1001605307.Es.r.html


> *Oxygen* makes up about 21% or *210,000 ppm *of the atmosphere.


CO2 constitutes 0.04% of atmospheric gases. At 760 mm Hg (sea level pressures), this amounts to 0.304 mm Hg. We're dealing on mm Hg (milimeters of mercury) since solvation of gases in liquids is based upon the concept of partial pressures.

It's true that there is about 300-400 ppm of CO2 in atmospheric air, but how does that compare with 210,000 ppm of oxygen gas? Or roughly 790,000 ppm of nitrogen gas? The partial pressure of CO2 is comparatively very very low in atmospheric air.

That's why even though there's 300 ppm of CO2 in the air, only a few ppm will actually dissolve in our aquariums.

As the CO2 in the aquarium comes out of solution into the air space within the drop checker, the partial pressure of CO2 in that air space rises dramatically because of the confined space. This increased partial pressure of CO2 in that space allows for a speed (within a few hours) equilibration between the drop checker liquid and the aquarium water.

When the drop checker is green, the water contains 30 ppm of CO2, which equates to a very high partial pressure of CO2 within that liquid. When you take it out of the water, this high partial pressure of CO2 within the liquid rapidly forces it out of solution to equilibrate with atmospheric CO2 which contains 300 ppm of CO2 but a very low CO2 partial pressure.

...hope that helps.


----------



## k-maub

That makes pretty good sense, but it also implies that in order to create the "very high partial pressure of CO2 within" the drop checker solvent, the drop checker's air would similarly need a very high partial pressure. Which to me would mean a much higher concentration than the normal 300 ppm atmospheric concentration, much less higher than 30 ppm...

What am I missing?


----------



## epicfish

Less oxygen and possibly less nitrogen in the drop checker air space would lead to an overall higher partial pressure of CO2 even though the CO2 amount is still 30 ppm.


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## banderbe

Now I remember why I got a degree in computer science instead of chemistry!

But seriously, instead of all the unnecessary rhetoric and quasi-scientific jargon, let's get to the point:

*your drop checker should turn blue if exposed to air for an hour or so.*

If it doesn't, you're doing something wrong. End of story.


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## k-maub

I suppose that much we can all agree on.

On the other hand, while I won't push the issue here, or at least start another thread to continue the conversation, I've always considered that one of the great things about this hobby is all the inadvertant knowledge from seemingly disparate fields one is exposed to.

That being said, I won't lead this thread further down this tangent; I very much appreciate the replies, especially the one to my original question.

Thank you.


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## dennis

Barry- YES

Epic, excellent and thorough job describing that, thank you!

One last thing then I will stop and let you get back to the fun part of making these things.... In response to k-maub's last post: Again, its partial pressure of the gas in liquid vs. the gas in air. At the surface of your tank, the CO2 is leaving the water and escaping into the air because the partial pressure of the air is less than in the aquarium water. Regardless of what ppm is in each, it is the "percentage" that epic described that leads to the difference. Your body works the same way by converting CO2 produced by muscles into carbonic acid for easy transport in the blood, then back to CO2 gas as it exits the capillaries in the lungs. The ppm concentration of CO2 (or carbonic acid HCO3) in the blood is much lower than the atmosphere but the pressure in the blood is higher, so CO2 readily transfers across the capillary walls and exits the body. With the drop checker, you have a similar situation. The little air space essentially is like the top of the aquarium and forces the dissolution of CO2 because of that. In addition, because it is a closed space, the CO2 concentration in that little gap is the same in ppm as in the tank, a much lower amount than in the atmosphere and a much, much lower pressure . In theory, this would make the drop checker work even faster underwater, of course it has to redissolve into the water of the checker which slows things back down again.

Sorry.


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## Squawkbert

OK - you've all covered this quite well and have made me ashamed at how much of this type of chem. I've forgotten.

The only little correction I can offer now is with respect to pH of carbonic acid solutions. Carbonic acid is a weak acid, so it will bottom out w/ respect to pH somewhere around 5.

Good discussion!


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## gforster

OK, I just got through reading the last 28 pages - whew! here's something maybe you can put into plain english for me. I would think most of us have scales for our ferts to measure things out. Many, like myself, are dosing PPS-pro where we have a nice solution in 1 liter bottles. Can you give me a "recipe" for 3dkh, 4dkh, and 5dkh solutions of distilled water in a 1 liter bottle?

For example - 


desired dkh- 3dkh 4dkh 5dkh
distilled water- 1 liter 1 liter 1 liter
baking soda - ??? ??? ???

This way there shouldn't be so many people saying, "I didn't realize how little baking soda it took." Instead they can get it pretty accurate from the get-go. You could then double check from there and test to make sure. I've seen something that resembles math in some earlier posts, but I can't figure it out. Me and numbers just don't go together. You really have to spell it out for me. Anyway, thanks for the help.


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## hoppycalif

Baking soda is not an exact crystal form of a chemical compound. It can have lots of water incorporated into the structure or very, very little. And, that affects the weight of a given amount of bicarbonate. Also, sodium bicarbonate can contain some sodium carbonate, which changes the percentage of carbonate per gram. (If you heat baking soda to dry it, you also convert part of it to sodium carbonate.) So, it isn't possible to specify with great accuracy what weight of baking soda to mix with a liter of water to arrive at 4 dKH. But, if you buy a certified KH solution, whatever the KH is, you can accurately dilute it with distilled water to arrive at 4 dKH with good accuracy. That is how the 4 dKH solutions we can now buy are made.


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## mhoy

> One teaspoon of baking soda will increase the hardness of 50 liters (13 gallons) of water by about 4 dKH.


See The Krib CO2 FAQ


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## Squawkbert

Assuming your baking soda is anhydrous (don't bake it out, undesirable chemistry will occur) - best to use a new box, dig down a bit...

I think these are the corrected values...
60.06mg per liter of RO/DI water = 4dKH
74.60mg per liter of RO/DI water = 5dKH

Now let's assume you don't have a balance that can accurately weigh out mg.
So the alternative is to make a more concentrated solution, then dilute.

6.0g per 5L RO/DI water = 80dKH (we'll call this the stock)
(1.20g in 1L will also work, if your balance is accurate enough)

1 part stock diluted to 20 parts total volume = 80dKH/20=4dKH - even multiples will also work. For example, 10mL stock + 190mL RO/DI=200mL total at 4dKH

25 parts stock diluted to 400 total parts = 80dKH*25/400=5dKH that would be 25mL stock + 375 mL RO/DI.


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## mhoy

Not sure if this would work. (Not sure which of the two holds onto water better though).
Save up some of those drying gels that come in the tiny packets. Dry them in a oven at low heat. Toss this into a sealed bottle, allow to cool then add some baking soda, wait a while and perhaps you have dry baking soda.


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## styderman

i got a scale for my guns and it goes to the .000 i think i put something like .029g in a gallon of distilled water. Correct me if this is wrong. It looks as if its working.


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## Squawkbert

styderman said:


> i got a scale for my guns and it goes to the .000 i think i put something like .029g in a gallon of distilled water. Correct me if this is wrong. It looks as if its working.


0.029g=29mg, 1g water = 3.786L

29mg/3.786L=7.659mg/L, assuming it's dry bicarbonate.
For 4dKH, you need 60.06mg/L of dry bicarb, more like 75mg/L if your bicarb is 19.5% water (like mine was).

If my math is correct, your chedker should be going totally yellow at the first hint of CO2 (green at 3ppm, what you would have w/o any CO2 addition) as you're in the 0.4-0.5dKH range.


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## styderman

hahahahahahhahahaloololloll i was wondering why it was always green. i turned the co2 up and many everything started to bubble. i got to leave my co2 running like 2-3 bps then everything starts to pearl. hahahahahahahahahahaha was wondering why it was always green. So how much do i put in one gallon. GRAM weight please.


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## hoppycalif

It is very difficult to get any accuracy making 4 dKH water with baking soda. I think I would rather trust a KH test kit instead, then just slowly adjust the KH until the test kit says it is 4 dKH.


----------



## turbomkt

Or get one of the 4 or 5 dKH standards that we see selling here and there


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## gforster

I just got one of the 4dkh standards and checked it against the test kit. It is accurate. Problem is, when I put it in the drop checker in the aquarium, it turns green, but I have no co2 in it yet. weird


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## kiwik

i made a bottle worth of this 4kh water, and then noticed i should be using distilled water. -.- i did it with distilled water, and i wanted to know if i can keep the extra water in a bottle in case i need it later. 
does the liquid in the bubble checker have to have kh test water and ph test water in it or just the ph test water?


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## hoppycalif

Just the pH test liquid goes in with the 4 dKH distilled water. What you are doing is measuring the pH of that bit of water, which will be about 6.6 when the color is green, and pH 6.6 plus 4 dKH equals 30 ppm of CO2.


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## kiwik

hmmm.....it's at night right now, and the checker is now tealish green. haven't seen it in another color yet besides the dark blue when it was just added. might be because it's been near a month and the ingredients all used up.


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## MyCatsDrool

Super easy drop checker recipe:

I made mine with an empty san fran bay glass brine shrimp egg bottle, a plastic 5 ml dropper, some silicone sealant and a suction cup.

Cut the 5 ml dropper squeeze part in half, then the long part to about 1.5 inches. invert, silicone into the opening on the brine shrimp bottle, with the long part on the inside. silicone suction cup to side of the glass bottle. viola.

Probably could do this with a test tube from a test kit too.

Cost: less than a penny.

cost me nothing since i have all this stuff laying around, all the time. And since the plastic 5 ml droppers are opaque, it is easy to see. And it looks really nice too. nice and small and unobtrusive, but if seen, not ugly.
I'll take a pic later and post it.


P.S. Thanks for the ideas and education. Never would have done it or thought of it on my own without this thread. I needed a drop checker badly for my ADA 5 gal and didn't really have the funds.


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## aquanut

so whats the highest KH people are using in the drop checkers and still seeing bba develop? 
using a drop checker with a KH of 4 im still seeing some BBA develop on the spray bars and co2 line...


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## hoppycalif

aquanut said:


> so whats the highest KH people are using in the drop checkers and still seeing bba develop?
> using a drop checker with a KH of 4 im still seeing some BBA develop on the spray bars and co2 line...


The drop checker just gives you a good estimate of how much CO2 is in the water. It does nothing itself for BBA, which I'm sure you already knew. This is a subtle hint for starting this thread in the algae forum.


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## aquanut

yeah i know that hoppy... my question was worded poorly, long weekend just got longer when i noticed the beginning of bba forming in a new setup. 

care to answer, what ppm are you shooting for these days?


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## hoppycalif

http://www.aquaticplantcentral.com/...trates/43026-riiver-silt-plus-soilmaster.html is what I am trying now.


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## aquanut

i see i see...


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## hoppycalif

There is always more to learn! Yesterday I found that the green color I was seeing for my drop checker was almost entirely a reflection of the plants color. When I pulled the little thing out of the tank, the fluid was very, very yellow! And, when I checked my CO2, I found that the tank was near empty. So, today, with a full tank I have been watching it more often - if you have enough pH reagent in it to get a strong blue color, you can easily see that it is green when it gets there. But, if you find you have to squint, move your head around, and work to see what the color is, it is very likely that it is yellow, which can be a very light color even when the fluid was very strongly blue to start with. Fortunately I didn't lose any fish this time, unlike the last time I ran out of CO2, and because I had 3 dKH water in it the actual amount of CO2 I had when it was so yellow was probably around 80-90 ppm, bad enough, but not a total disaster since I caught it pretty quickly.


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## tcfish

I would like to throw my hat in the ring when I first read this thread I had no idea what a drop checker was now I know and have built my own thanks hoppy


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## hoppycalif

tcfish said:


> I would like to throw my hat in the ring when I first read this thread I had no idea what a drop checker was now I know and have built my own thanks hoppy


You are welcome, and that is a nice looking job you did. If you now use white finger nail polish to paint the inside surface of that center tube you will have a nice white background to view the color against. Or, am I looking at it wrong? Is the fluid in the annulus or inside the small tube in the middle?


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## tcfish

what I did is take a small dowel rod put a slit in it an wrap some sandpaper around it like a 220 grit an sand the inside of the small tube to make it white so the color will show,actually emery cloth is what I used gives you a nice smooth surface and will turn that inner tube white like snow


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## tcfish

OH by the way hoppy love that pic on your avatar looks my uncle Joehoesafat !!! Kidding aside I am not kidding !!!


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## tcfish

Also annulus is that like corn hole Ha Ha Just a dumb southern boy being a smart as# no off course not water is around stem like I copied it from you.


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## hoppycalif

The sand paper idea didn't work well for me - the water makes the white become almost transparent. Nail polish is acrylic, the same material as the tubes, so it is the perfect "paint" for acrylic. And, that idea definitely works, if you can find white nail polish.


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## Blacksunshine

White acrylic nail polish is the way to go unless you can find white acrylic tubing.



tcfish said:


> I would like to throw my hat in the ring when I first read this thread I had no idea what a drop checker was now I know and have built my own thanks hoppy
> 
> http://www.aquaticplantcentral.com/...?attachmentid=5620&stc=1&thumb=1&d=1194151497


Nice work.  looks familar. Did you use the post from the airline hose? I found that they don't like to attach to the acrylic so well. (they are plastic not acrylic) So what I do now I cut acrylic rod the same size of the hole of the suction cup. It makes a MUCH stronger bond.


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## tcfish

Well I have to agree with the nail polish when it is all blue sitting in the tank all is well. But when that bugger turns color to green it get hard to really see if it is green or yellow .I put a white piece of paper behind it to see its true color. I can see it now "Honey were is your nail polish" her reply "do you want some lipstick too!" Also I used a heater holder cut it down and used weld-on #16 hope it holds up, but that is a great idea with the acrylic rod, and it just so happens I have some very small rod and I will go that route if I should make another or this one does not hold up.Thanks guys


----------



## Amazon_Replica

I have successfully made 4dKH water, and added ph solution and put it in drop checker, it is in the tank. Thanks a million Hoppy. I didn't think, even after reading this thread, that I would be able to do it. Wasn't as hard as it seemed it would be. Patience and distilled water lol. Thanks again it was easy with your instruction and everyones input!


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## Iceterran

Is there a certain time that is best to use the drop checker? It probably takes some time for the tank water to become saturated with c02 right? (sorry for the noobie questions, just found this thread a good chance to get them out there)


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## orlando

You just leave it in there as an on spot indicator..


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## Iceterran

Sorry this is repetitive, but just to clear things up, I can permanently leave the drop checker submerged in my tank and simply refer to it at any given time? (without ever changing the solution?)


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## hoppycalif

The solution contains a dye - the bromothymol blue dye that is the pH indicator reagent. Dyes do fade over time. Also, the drop checker will gradually accumulate biofilm and need to be cleaned thoroughly. Most people seem to be replacing the fluid and cleaning it about every two weeks.

It is intended to be left in the tank full time. If you remove it, the solution in it will start evaporating and that will make it inaccurate.


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## devocole

Okay so i made the very original rectangular drop checker out of acrylic and silicone sealant. The acrylic was from a clear picture frame. I worked out great. I think this one will just be a model because i would like to do a better job with the silicone. All i did to cut the acrylic was score it, and i snapped perfectly along the line.
Devon


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## hoppycalif

Silicone isn't the best way to glue acrylic, but if it works, it works. Let us know how this works in the aquarium. Are you going to attach a suction cup to hold it in the aquarium?


----------



## devocole

what would you recommend for acrylic?


----------



## hoppycalif

Acrylic cement is just a solvent that softens the acrylic, so it welds to another piece of acrylic. The high viscosity type cement has pieces of acrylic dissolved in the solvent, so it can also fill gaps or make filets at the corners. I use the high viscosity type. I buy it at the "Tap Plastic" store near me.


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## curt_914

I use Weldon 3 acrylic cement I get from my local distributer, you should be able to order from them online here;
http://www.plasticareinc.com/Merchant2/merchant.mvc

You may have to e-mail them for priceing and avaliability. Also here is the info on it;
http://www.ipscorp.com/industrial/acrylics.html

Curt


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## devocole

You guys were right, the silicone leaked. I tore it apart, and used acrylic epoxy and here it is. I'm going travelling so i won't try it out for 4 months, but i'll post something when i do. Thanks


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## sebas

here my DIY drop checker

Material:
Silicone
funnel
test tube
white enamel
suction pad


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## hoppycalif

Wow! I'll bet high school chemistry labs will all be short on funnels and test tubes now. That one is an extremely easy to make variation, and good looking too.


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## Bk828

Thanks for the ideas. Great thread


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## Brendan Redler

hoppycalif said:


> The reason for setting the KH of the indicator solution to 4 is so that with 30 ppm of CO2 the indicator color will be green, and an unequivocal green. That gives the maximum accuracy. If you had a lower KH, the 30ppm color would be near yellow, almost impossible to judge, and if you had a higher KH, the color would be blue green, again very hard to judge. Actually, any KH that is within .5 of 4.0 will work, but 4 seems to be just about the perfect KH. Since it is easy to get the KH to whatever you want it to be, as accurate as you want it to be, why not shoot for 4.00 KH? (You can even use 10X the usual water sample size, so that each drop of KH solution will equal .1 degrees of KH. I used 4X and could judge it even closer by noting how nearly each drop came to tipping the color over to yellow. (I use AP test kits)


I know that this is a dead thread...but I couldn't help myself. If you are interested in the dilution practice that hoppy is using, look up the principles of *titration*. It's exactly what he has described here and you'll feel all smart and sciency and stuff. I'm a chem major and I'm glad that I'm seeing people titrating things!


----------



## zer0zax

Thanks so much Hoppy, and everyone else who posted ideas and questions in this thread. I had no idea how a drop checker worked, but all of my questions are already answered!

Someday I will try Sebas' style of drop checker, nice clean and easy. just wondering if anyone has tried using 2 drop checkers in one aquarium, 1 w/3dKH + 1 w/4dKH? 

Is it possible to get an accurate reading in between them?

Thanks again!


----------



## Squawkbert

^ not really, though together, they will cover a larger range. The 3dKH one will cycle from blue to yellow and stay yellow as the 4dKH one starts to think about going green. I guess if 3d is yellow and 4d is blue, you're somewhere near 10-15ppm(?-been a while since I looked at the charts).


----------



## zer0zax

^^I think this would show 20-30ppm Co2, but I plan to run DIY Co2, so the 10-15 range is what I would really expect. You have a real good point though, the in between numbers like 15ppm or 25 ppm would be to much of a pain to try and decipher. As long as I can get above 10ppm for a lowlight I will be happy!


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## dawntwister

I see a lot of simple designs for the drop checkers but I don't see any mention of where to buy the fluid to put in the drop checker. Where do you buy the fluid to put in the drop checker?


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## pepetj

dawntwister said:


> I see a lot of simple designs for the drop checkers but I don't see any mention of where to buy the fluid to put in the drop checker. Where do you buy the fluid to put in the drop checker?


You DIY!

Use distilled water and add tiny-tiny amounts of baking soda. By trial and error, take samples of your water and measure until you know you have a 4 dKH solution. If you use 10ml of water as sample instead of 5, your reading will be more accurate; just divide by two the number of drops you added until the color changed. Once you get it dump the sample you added the KH reagent to, use your solution to add some drops (I like adding at least 7 of bromthymol blue) pH reagent solution and insert it in your DIY drop checker device.

Pepe
Santo Domingo


----------



## lovingHDTV

Looking at some of these designs I would like to offer up another idea.

Why not use a test with a single hole rubber stopper. The insert a glass tube into the hole. Invert the whole thing and your done.

I was looking around and you can buy these parts for < $5.

The only question I have is the effect the rubber stopper would have on the solution.

Comments?


----------



## dawntwister

Sounds like a niffty idea. Where do you get the rubber stoppers?


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## lovingHDTV

These guys have it all, but are out of stock on the tubing.

http://www.crscientific.com/stoppers.html


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## lildark185

I made a DIY drop check which holds very little water ~0.75mL. Would this work?


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## pepetj

The amount of water you use will not matter as long as you keep some air trapped between the two fluids (#1. water tank; and #2. 4dKH -sodium bicarbonate solution in distilled water- with a few drops of pH reagent).

Pepe
Santo Domingo


----------



## pepetj

lovingHDTV said:


> Looking at some of these designs I would like to offer up another idea.
> 
> Why not use a test with a single hole rubber stopper. The insert a glass tube into the hole. Invert the whole thing and your done.
> 
> I was looking around and you can buy these parts for < $5.
> 
> The only question I have is the effect the rubber stopper would have on the solution.
> 
> Comments?


I used a catheter (medical use rigid plastic tube for Intra-Venous administrations) and a glass test tube. Here is a pic of one I just made. I am working in a smaller unit now.


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## Jebadiah

FYI, in case you don't want to or don't have the equipment to make up your own batch of 4dKH, I am selling the remainder of my last batch on Ebay. It is cheap, just looking to cover my time and costs, not make a huge profit.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MESELX:IT&item=320329616880


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## fjr

my friend came by and i showed him this thread he came by the next day with this what do you think?


----------



## stepheus

pretty good really.


----------



## agy

My DIY is very simply

This is my personal idea, please respect 

From some test kit plastic pipette, cut off only narrowest end of a pipette, mix 1-2ml 4dkh water with 1-2 drops test solution, after water blue take all mixture inside pipette and put down in to aquarium with open end and fit in to some sucker mount, if too big - cut piece of silicone tubing, Pull on legs of a sucker to fix a pipette. Also be convinced that air between a liquid and water is present
Easy tricky setup just in few minutes.


----------



## dawntwister

fjr said:


> my friend came by and i showed him this thread he came by the next day with this what do you think?


You can make something smaller using a ball that you get in candy machine which has a toy in it.


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## agy

I don't trust to drop checkers. Too slow reaction and not so correct, sometimes i think my eyes are wrong, lol.( I found info in internet - Japan people see much more colors and tonalities as White Europeans !) This piece is nice, but need check ph minimum 2 times every day. Drop checker can show green but ph can be much lower.
And if will be some electrical shortcut or lights go off - overdosing, disease - fish can die,algae, ...
I bought digital ph meter for self in Ebay for 23 GBP, highly recommended.

Plese look chart standard co2 test solution what use all drop checkers - bromothymol blue










green on PH 6.4 can be too low and can be too late - overdosing, i keep min. 6.6ph and in morning before co2 on is 6.8
Situations is different, possibly 6.4 can be fine, depend from many factors kh,gh, temperature,..
My info just for reference, i hope this info helps avoid some mistakes

I tried once shut off at 6.3ph co2 and switched on air pump with open top of aquarium and for raising in 44gal tank ph from 6.3ph to 6.6ph needed half day

Very carefully with all co2 things
Also almost all ph tests is wrong +-1,2 due different temperatures or have color scales like 6.4:6.8:7.2 - potencial overdosing or too low level
I highly recommended digital ph meter with ATC(Automatic temperature control), once calibrated shows very exact ph longtime +-0.05

Fish Health is more important, and i don't understand why need extreme fast growth if later plants throw away


----------



## LuisVillalobos

pretty kool


----------



## Fat Guy

does the hole that lets the co2 in when submerged need to be a specific size. The diy one that I built has a channel with an opening about the size of a pencil tip for the co2 to travel up to fill the chamber with the blue 4dkh water in it. I guess my question is do you think this will be effective? My thoughts are that it will take more time because the hole for the gas to travel is smaller, but I still think that it should work. Any thoughts? I'll post pics in a sec.


----------



## Fat Guy

Here's what I did. It's from a journal I keep in another forum so sorry if it's wicked pic heavy:

I was bored today and wanted to build my own DIY drop checker. So I used an old scented oil container, mixed up a batch of 4dKH and went to town. Here's some photos. My only concern is that the modified plastic tube is too small and will take a long time for the gas to change the color of the ph reagent. I'll wait till tomorrow to see what becomes of it. But since I've put it in, I haven't been noticing any real significant change in color. Could it be that even with the pressurized setup, I'm not pushing that much CO2 into the water? Will I have to kick it up a notch? stay tuned.....

Here's what I did:










took the plastic wrapping off, boiled it and scrubbed all the oil off of it.









removed the oil distributor, my idea being that I could use the small pin hole channel for the gas to travel up and into the basin.

















took some sun cure resin that I use to repair the dings on my surfboards and filled in a hole on the distributor. (this one comes with two channels. One that is positioned in the middle of the plastic, and another one that is positioned deeper and travels the length of the plastic shaft. If you happen to see one of these containers, twist off the top and look at the holes and you'll see what I mean. 
Here's what I used to seal the one hole so that I could create a basin.








Here's the section I filled in:








used a suction cup setup that you can get at your LFS that will fit around a 1"heater. Fit like a glove. Then stuck it to my window in my dining room...just for good measure.








You can see the plastic channel better here. 
got some distilled water








mixed in some baking soda and tested and tested and tested until I got roughly 4dKH-4.5dKH. Added .2ml 4dKH water with a baby dosing syringe and 4 drops of pH reagent.
Then carefully put it in my aquarium.
























finishing touches...









Now, the issue that I'm having is that the drop checker solution is still blue and does not look like it has changed. It's been roughly 3 hours. I'm about to hit the hay here and will revisit the project in the morning. I have another option that I can use, but I like the way that this looks compared to some other diy setups that I have seen. I may run the second one I made next to this one to see if the gas really is making its way up the chamber. I used .2ml 4.5dKH and 4 drops pH reagent for the solution. I moved the drop checker to the far left corner under the glass and cranked the filter up to move the bubbles around. so far so good. just wait...after running the pressurized for this long, I'm gonna be kicking myself a little if I find out that I need to add more....at least the fix is an easy one. Just open up the needle valve a little and see where that takes me. After all...it's only moss were dealing with here.

Thanks for looking and any advice on my drop checker dilemma is much appreciated. Really thankful for the great tips in this thread. If mine is fully functional I'll be glad because it doesn't look too DIY.

-el g


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## Fat Guy

Overnight Success!!


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## fishlegs

Fat Guy said:


> Now, the issue that I'm having is that the drop checker solution is still blue and does not look like it has changed. It's been roughly 3 hours.


I'm guessing your design would take longer to show changes because the water/air interface is so small. It will take gas longer to reach equilibrium. This is the reason the commercial drop checkers have the bell-shaped horn... the half-dollar sized area where the water and air meet allows CO2 to diffuse more quickly into the air pocket. The size of the air pocket might also matter (seems a smaller air space would transfer gas more quickly?) but not sure.


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## bartoli

A key to speeding up the reaction time is reducing the air space in the bottle. For example, you can use the sun cure resin to fill up much of the bottle.

The less air in the bottle, the faster it is for the water CO2 to reach the 4 dK solution.


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## Fat Guy

bartoli said:


> A key to speeding up the reaction time is reducing the air space in the bottle. For example, you can use the sun cure resin to fill up much of the bottle.
> 
> The less air in the bottle, the faster it is for the water CO2 to reach the 4 dK solution.


that makes perfect sense. It's not perfect yet, but as it is, it does the trick. Thanks for the replies. Best,

el g


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## Fat Guy

I've had a lot of free time the past couple of days. And with the rain in NYC, I've been spending a lot of time working on the aquarium. I wasn't happy with the drop checker chamber so I decided to make it bigger, without making it over complicated. It was taking way too long to get readings with the drop checker and I felt like it was because the gas wasn't traveling very rapidly into the chamber with the reagent. So I removed the cap, and took half inch airline tubing, cut it to size, and fit it through the opening in the glass vial, filled the container with approximately 3ml dKH4/4.5 H2O, added 6 drops pH reagent, tested the seal, and placed it in the aquarium. It went a little something like this.








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## Fat Guy

Success in just under 3 hours!!

The new modification works like a charm:








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## virgo888

good idea though. i got lazy and bought one - works great after i made my 4dkh solution.


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## Fat Guy

virgo888 said:


> good idea though. i got lazy and bought one - works great after i made my 4dkh solution.


thanks. this drop checker works like a charm. if yours breaks...try this modification on for size.

best,

el g


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## dzsenci

hi 
im new and imi thinking 
i got KH tester 
if i test my wather and then i put ph reagent from the ph tester , is that liquid good 4 the drop checker ?


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## dzsenci

how offen u need to change the solution from the drop checker?


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## dzsenci

no one changes the solution from the diy drop checker ?

i have 1 more problem 
we use 4 dKH water , and i use 10 drops of PH reagent on 2 ml dKH water , and it's still not blue ,is a dark green .
why is that ?
what we do wrong ?


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## pat w

Are you using tank water, or a prepared 4dkh solution?

If tank water, stop the practice and get or make a reference solution. Tank water will give you unreliable results. The 4dkh in a drop checker must be exclusivly from carbonate, nothing else.

If you are already using a prepared solution and it was homemade (baking soda and distilled water) you may have had some moisture in the baking soda (it can hold a lot). You need to bake it in an oven (325 F for an hour or so) then weigh it out for the solution. I made this mistake and got basically the same type of results you described, a greenish blue instead of blue when I added the PH reagent. It will cause you to misread the CO2 in your tank, thinking it is high enough when it's really too low. My result ... algae bloom.

Pat


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## dzsenci

hi 
i am using a prepared 4 dkh water
the water was made in a lab from baking soda an distilled water 
i use 2 ml of 4 dkh water and 10 drops of sera ph reagent and it turns green not blue 
i see on youtube some 1 use 4 drops of ph reagent and turn blue 
it can bee the moisture ?
i will tell 2 mi friend 2 redo the 4 dkh water 
not even now after 2 days of using it diden't change 2 much the color 

i test my water and i have 6 ph , but the drop checker is almost green and the test shows me almost yellow . if i am not wrong it has 2 be both the same color . i am right ?
that meens that the solution from the drop checker is not good?


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## pat w

dzsenci,

The solution in the drop checker and the tank water are independant of each other. The two should test differently.

I'm starting to think you may have some misconceptions about how a drop checker works. Add to that the fact that all information reguarding them is in English. Sorry, but I can't help there but, I can offer what is concidered by many a very good post on the subject. Read it over and then get back with any questions you may still have.

http://www.barrreport.com/showthread.php/2818-Drop-Checkers-CO2-Indicators-Why-and-How?highlight=drop+checker

Pat


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## dzsenci

i know that the solution and the tank water are independent 
i read a lot about the co 2 checker before i start to use one , but i that is better to ask because some of my friends told me that is possible to use the solution from the drop checker too test the water ph . 
my drop checker works , because it change the color to yellow green (that to much of co2 , i know that , i am traing to reduce that )
mi problem is that my water that i use is only 3 Kh strong , and i need to raise a little bit the ph because it's to low ( 6 ) . 
that why i wondering of good working about the drop checker because watching the ph/kh/co2 table it's not good


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## pat w

Bottom line on drop checkers with 4dkh solution and standard PH reagent is that they turn blue initially and change to green or on to yellow acording to the CO2 content of the tank water. If your DC is already showing some shade of green initially then either the solution is not at 4dkh or your reagent is old or off in some way. Bromothymol blue added to the DC should indicate a PH of near 7.6, blue on the chart. 1 full point of PH down to 6.6 will take it to green. If you can't trace the discrepancy perhaps you can try to determine what PH your initial test indicates and what 1 full point of PH drop should show in terms of a color change.

Pat


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## gh0ul

The sera ph Reagent does not use Bromothymol blue. THis is why it turns green. 

IT WILL NOT WORK LIKE OTHER pH REAGENT


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## HeyPK

> The sera ph Reagent does not use Bromothymol blue. THis is why it turns green.


Bromthymol blue changes from blue at pH 7.4 through green at around pH 6.6 to yellow at pH 6.


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## zhanghanbing

pics not showing


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## HeyPK

What pictures are you talking about? What posts?


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