# co2 drop checker



## ponyrandy (Jan 13, 2007)

I am about to change from fermentation co2 to pressurised. After reading the previous post I think I should probably get a drop checker also. Sorry to hear of the loss. Would someone please do a thread on how a drop checker works and include photos if possible. Do they require maintenance or once they are in they are good for a while? What happens when doing a water change and the water level drops below the drop checker?

Also on a related note, what about ph controllers? I see you have to use calibration fluid, how often does this need to be done? 

Thanks, Brian


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## goalcreas (Nov 20, 2006)

Here is a thread with a great deal of information on them

http://aape.naturalaquariums.com/forum/index.php?topic=759.0

Here is another one telling about the importance of using a known DKH solution in the drop checker

http://aape.naturalaquariums.com/forum/index.php?topic=1111.0

Hope these help, any more questions feel free to ask


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## ponyrandy (Jan 13, 2007)

Thanks for the info! I will sit down and read.
Brian


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## ponyrandy (Jan 13, 2007)

Great read! Lots of good information. Thanks again goalcreas.
Brian


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## imzadi (Apr 3, 2007)

I'm doing the same thing as you, switching to pressurized, and my drop checker should arrive tomorrow. I went for the cheap red sea CO2 indicator, I can always get a pretty and expensive one later. I'm also going with the known KH water for the indicator, because I have REALLY high KH here in SE New Mexico. I really hope it works, because guessing is scary! 

BTW, the solution in the drop checker lasts 2 weeks to 1 month in your tank, depending on who you ask. Kept separate, the KH water and the reactor fluid keep indefinitely.


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## Muirner (Jan 9, 2007)

imzadi - How come the solution once in tank becomes no longer reactive and must be changed? I'm getting a drop checker in hopefully next week to match up with the CO2 equiptment and ferts i have freshly aquired. I was thinking about that today, how could the fluid stay "good" or how long does it stay good?


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## freydo (Jan 7, 2006)

according to this thread:
http://www.aquaticplantcentral.com/...aquarium-projects/32100-diy-drop-checker.html

you're probably good for about two weeks, but that's different for everyone. you could probably get away with a month or so before you have to change the solution. it just depends on much colour is retained in the solution, and if you're able to read the colour properly.


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## goalcreas (Nov 20, 2006)

You can go longer, but it is so easy to change, why not just do it every time you change the water.
The price for the reagent is tiny and the time it takes is what 5 min tops. (probably more like 2 min)

If you are using a pre-made purchased solution for your drop checker water it may up the price a little, but you get 500ml, and you use what 2ml in a drop checker so you get 250 uses, and at $7 for the bottle then you are using 2.8 cents per use, and adding shipping might double it so you are at 5 cents.

Bottom line, why not change it and be safe?


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*

I have a question about the procedure to replace the known KH solution in the drop checker.

Should you just empty out the old solution and add some fresh solution or should you clean it with RO/distilled water and make sure that it's completely dry (no water in it at all) when you add fresh solution?

It seems to me that if some of the old solution is left in it, it might skew the validity of it's reading.

If the solution is replaced frequently when you do the weekly water change, it may have no effect on it's reading. Just wipe it out if you can and add fresh solution.

Also, if you clean it and you don't have it completely free of any water when you add fresh solution, it will definitely skew the reading.

Any thoughts? I haven't read anything about this.


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## Blacksunshine (Aug 11, 2006)

Nahh you can go a few months between changing your soloution. I placed one of my DC's in my tank a couple months ago and if I haden't replaced the DC with one of my newer builds I'd still be using it.
500ml of DC regent would last you a VERY VERY VERY VERY VERY long time.


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## goalcreas (Nov 20, 2006)

Well, it is a visual aid, it is a drop "CHECKER". It is not exact in any sense of the word and there are many variables that can skew it's reading.
For instance, I have a tank that is kept at a PH of 6 and for this tank, the drop checker is completely useless, when I put it in with zero CO2 in the tank, the drop checker turns yellow and there is like I said zero CO2 that I have added.

If you want it completely accurate, it will take some time setting up, constant watch on the parameters of your tank and a bit of calculations. But for most of us, just being able to see what is going on kind of helps, but is not that accurate.

You are right to assume that is you leave solids in your drop checker and ass solution that you will have more DS in your solution then you started with, but probably not all that much, that being said, you shouldn't go without cleaning it for very long. If you were to do it quickly 3 weeks in a row and then on your 4th week, when you are cleaning your filter lines, filter, maybe just doing a more complete clean up, then you can go and really clean the drop checker, that should be enough to keep the "ROUGH ESTIMATE" that it is, going fine.


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*



goalcreas said:


> Well, it is a visual aid, it is a drop "CHECKER". It is not exact in any sense of the word and there are many variables that can skew it's reading.


That's true because you don't have an exact color reference to go by. Like the ones that come in test kits.


goalcreas said:


> For instance, I have a tank that is kept at a PH of 6 and for this tank, the drop checker is completely useless, when I put it in with zero CO2 in the tank, the drop checker turns yellow and there is like I said zero [email protected] that I have added.


Could you use a known drop checker solution with a KH of 1? With a KH solution of 1, you can have a:
pH of 6.0 with 30.0 ppm of CO2
pH of 5.8 with 47.6 ppm of CO2
pH of 6.2 with 18.9 ppm of CO2



goalcreas said:


> If you want it completely accurate, it will take some time setting up, constant watch on the parameters of your tank and a bit of calculations. But for most of us, just being able to see what is going on kind of helps, but is not that accurate.


I like to just be able to see what's going on too.



goalcreas said:


> You are right to assume that is you leave solids in your drop checker and *ass solution* that you will have more DS in your solution then you started with...


 I just about fell out of my chair when I read this because I was laughing so hard. I'm sure extra *ass solution* would make a difference.[smilie=l:


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## goalcreas (Nov 20, 2006)

Whoops


Add Solution

I am sure you knew what I meant, but it was funny, americas funniest typo's season 1


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## goalcreas (Nov 20, 2006)

So If I use a solution (double checking not to do another ASS SOLUTION) with a KH of 1 and am at 6.0 ph, then without even adding co2, my drop checker is yellow, but by your calculations that would mean that I am at 30ppm CO2.? Or would the drop checker solution not be yellow with the KH 1 solution and a PH of 6.0?
So if I dropped to 5.8 then would I have 17.6ppm and would I have to drop to 5.5 to get the required 30ppm?

This is not an answer, it is a question


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*

That was funny!

My numbers came from playing with Chuck's CO2 calculator: http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

I took it that you kept your tank at a pH of 6 by using CO2 and you probably have a low KH in the tank too.

With a known KH of 1°, your drop checker solution should be green indicating 30 ppm of CO2. Chuck's calculator shows that with a pH of 6 and a KH of 1° that the CO2 level is 30 ppm.

A yellow color will show a lower pH and a higher CO2 level and a blue color will show a higher pH and a lower CO2 level. I picked the pH numbers of 5.8 and 6.2 as just examples of the changes in CO2 levels. I don't know the exact pH that the colors will change.

It's the same principle as using a known KH of 4° that indicates a green color of 30 ppm of CO2 and a pH of 6.6. Only the KH was changed so that you have 30 ppm CO2 at a pH of 6.

If you have a little different situation in your tank like you mentioned in the last part of your question, you can play around with some numbers to find the correct known KH solution for your tank that will indicate the optimum ppm of CO2 that you want.

I hope my rambling makes sense. I just got through pigging out and I can't think straight.


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## Squawkbert (Jan 3, 2007)

Changing solution is a function of how much indicator is in yours and how much light it gets.
Light eventually starts to break down the indicator, so it fades. When this happens, it's time to change. I've had some go south in a few weeks (all glass, mounted ~8" below a 96W PC) and I've had some go a few months (mounted lower under a lower wattage bulb). YMMV.

As to change procedure, I'd dump the contents of the old one, give it a little rinse w/ some of the standard dKH solution of your choice, then refill w/ indicator solution (this assumes you have some straight 4 or 5 dKH solution and some of the same premixed w/ indicator - if you only have premixed, just rinse w/ a little of that).

And yes, you make your dKH according to your CO2 target. 4dKH for most of us, 5dKH for people that want at least 30ppm CO2 (may even be higher - am not looking at the chart now),


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*



Squawkbert said:


> Changing solution is a function of how much indicator is in yours and how much light it gets.
> Light eventually starts to break down the indicator, so it fades. When this happens, it's time to change. I've had some go south in a few weeks (all glass, mounted ~8" below a 96W PC) and I've had some go a few months (mounted lower under a lower wattage bulb). YMMV.


That's very good info.



Squawkbert said:


> As to change procedure, I'd dump the contents of the old one, give it a little rinse w/ some of the standard dKH solution of your choice, then refill w/ indicator solution (this assumes you have some straight 4 or 5 dKH solution and some of the same premixed w/ indicator - if you only have premixed, just rinse w/ a little of that).


I didn't think of rinsing it out with fresh dKH solution. I like this method.



Squawkbert said:


> And yes, you make your dKH according to your CO2 target. 4dKH for most of us, 5dKH for people that want at least 30ppm CO2 (may even be higher - am not looking at the chart now),


Thanks for the very good info, Squawkbert!


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*

I should of mentioned this last night, but I was sleepy and tired with a full belly.

I would assume (ass-u-me) that there's a lower limit of the KH value where the buffering capacity of a known KH solution would be unstable and the accuracy of making that low known solution would be hard to make at the general hobbyist level. Also, what would be the lowest known KH value that would be usable for a planted aquarium? I don't know that exact value.

The formula is exponential (it's based on 10 to the -7 power). This means that the concentration of CO2 varies very little with small pH changes at the higher KH values. It's the exact opposite for lower KH values. The CO2 concentration varies tremendously with small pH changes. You can easily see this when you look at Chuck's graph. http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

Here's three examples:
1) pH 8.0 - KH of 0.5° = 0.15 ppm CO2 & KH of 15° = 4.5 ppm CO2, so a KH swing of 14.5° only changes the CO2 concentration by 4.485 ppm
2) pH 7.0 - KH of 0.5° = 1.5 ppm CO2 & KH of 15° = 45 ppm CO2, so a KH swing of 14.5° changes the CO2 concentration by 43.5 ppm
3) pH 6.0 - KH of 0.5° = 15 ppm CO2 & KH of 15° = 450 ppm CO2, so a KH swing of 14.5° greatly changes the CO2 concentration by 435 ppm

So what I'm saying is to be careful with low pH and KH. It can get you in trouble with high CO2 with tiny changes.

Here's some more ramblings. (Thinking about an old Marshall Tucker song that says, "I got ramblin' on my mind.")

I looked around on the web at various charts and the lowest KH value shown was 0.5° and with a pH of 6, the CO2 level was 15 ppm.

I'm playing around with the numbers on Chuck's calculator again trying to find a low KH value and a low pH that would come out to ~ 30 ppm of CO2.

By using a known 0.5° KH solution, a pH of 5.7 gives 29.9 ppm of CO2. So, by making a known KH solution 0.5°, the indicator color would be green showing 29.9 ppm of CO2 at a pH of 5.7.

I don't think that this would be practical or useful, but here's another playing around with numbers example using Chuck's calculator. Let's say we can make a known KH solution of 0.1°. the green color would indicate 30 ppm of CO2 at a pH of 5. (I'll bet that if we could do this in an aquarium that the indicator color would be changing back and forth so much that it would be like a blinking light because of minor changes in the pH at this KH level causes huge swings in the CO2 concentration.)


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## ponyrandy (Jan 13, 2007)

goalcreas said:


> Well, it is a visual aid, it is a drop "CHECKER". It is not exact in any sense of the word and there are many variables that can skew it's reading.
> 
> Thanks for the discussion, I have learned a lot. With all of this being said, I think I will forego the drop checker for now and try the 'seat of my pants method'. One of the reasons I am changing to pressurised is to minimize maintenance. I figure once I get the bubble rate set, with a 10 pound tank on a 25 gallon aquarium, I can make it the better part of a year before having to do anything. If I include a drop checker into the equation I then just shift the maintenance from the ferment bottle to the drop checker. The other reason I am going to a pressurised system is to get some consistency with the co2.
> 
> ...


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*

Hi PonyRandy

I thought this was a good discussion too.

Here's my thoughts on your plan:
- going pressurized is great, all my tanks are pressurized now; DIY was a PITA for me
- be sure that you get a good quality regulator that has a very good needle valve
- get good CO2 tubing and a good quality check valve, like a brass one
- you'll need a bubble counter
- use the diffuser/reactor of your choice or you can plumb the CO2 tubing into some types of filters
- I recommend that you do get a drop checker with a known dKH solution from someone like billionzz, flying by the seat of your pants can be problematic sometimes
- I use Milwaukee pH controllers and I like them, but they aren't a necessity; they are a luxury item
- good luck!


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## ponyrandy (Jan 13, 2007)

This being my first attempt at pressurised, I have done a lot of looking at regulators and reading threads. I ran across this regulator:
http://www.aquariumplants.com/AQUARIUMPLANTS_com_s_Co2_Regulator_The_BEST_p/co2-1.htm
and liked the price, the warranty, and just the overall looks. It does seem to have all of the right components that everyone seems to like. I have not seen anyone mention this particular setup though. To avoid changing the direction of this thread I will repost to see if anyone has any experience with it or not. Anyway I have already ordered one and I will post once I get it and get it hooked up. 
Thanks again, Brian


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## Squawkbert (Jan 3, 2007)

*Re: CO2 drop checker*



Left C said:


> ...The formula is exponential (it's based on 10 to the -7 power). This means that the concentration of CO2 varies very little with small pH changes at the higher KH values.


Basic problem... you're talking about using charts, pH and KH. KH is tough to measure correctly because carbonate anion is pretty much never the only thing buffering aquarium water. This makes the charts/pH method of measuring CO2 highly suspect.
The pH and KH of the tank water are what they are and your CO2 level doesn't change unless you change your addition and/or uptake rates for CO2. In other words, you do not get more CO2 into your water by screwing around w/ your water's pH & KH. Ever.

pH is not an exponential function, it's logarithmic. pH=-log[H+]

The beauty of the drop checker is that you isolate your 4dKH standard solution in the checker. The aquarium water pH, dKH etc. just does *not *matter at all.

When the gasses dissolved in the tank water reach equilibrium w/ the air in the drop checker, the checker will tell you how much CO2 is in the water as a function of the change in pH *within *the drop checker. 4dKH water has a pH a little over 7. Adding 15-30ppm CO2 to the system drops the pH to 7 (or a hair lower - enough to make the solution green). If you want the thing to go green at a higher level of CO2, you increase the dKH *inside *the checker. This raises the starting pH a little more so more CO2 is required to drive it back to green. As long as you make a good standard carbonate solution, you will have a highly accurate, reproducible reading.

The tricks to making the reading show up with less lag time are in the checker design. You need to have low air volume above the indicator solution, high surface area between the air & solution and high surface area between the air and the aquarium water. You also need to have enough indicator solution so that you can see the color change, but less solution=faster readings.

If you're going pressurized, I'd strongly suggest getting a drop checker.


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## Left C (Jun 14, 2005)

ponyrandy said:


> This being my first attempt at pressurised, I have done a lot of looking at regulators and reading threads. I ran across this regulator:
> http://www.aquariumplants.com/AQUARIUMPLANTS_com_s_Co2_Regulator_The_BEST_p/co2-1.htm
> and liked the price, the warranty, and just the overall looks. It does seem to have all of the right components that everyone seems to like. I have not seen anyone mention this particular setup though. To avoid changing the direction of this thread I will repost to see if anyone has any experience with it or not. Anyway I have already ordered one and I will post once I get it and get it hooked up.
> Thanks again, Brian


I have it and I'm not very happy with it. I'll post why in your other thread.


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*



Squawkbert said:


> Basic problem... you're talking about using charts, pH and KH. KH is tough to measure correctly because carbonate anion is pretty much never the only thing buffering aquarium water. This makes the charts/pH method of measuring CO2 highly suspect.
> The pH and KH of the tank water are what they are and your CO2 level doesn't change unless you change your addition and/or uptake rates for CO2. In other words, you do not get more CO2 into your water by screwing around w/ your water's pH & KH. Ever.


You may be missing what I was explaining to goalcreas. I was referring to the known KH solution in the drop checker and not aquarium water. The chart is valid by using a known carbonate KH solution.

I don't know if you read this part or not but goalcrse said this:


goalcreas said:


> ...I have a tank that is kept at a PH of 6 and for this tank, the drop checker is completely useless, when I put it in with zero CO2 in the tank, the drop checker turns yellow and there is like I said zero CO2 that I have added...


Then my response was: 


Left C said:


> ...Could you use a known drop checker solution with a KH of 1? With a KH solution of 1, you can have a:
> pH of 6.0 with 30.0 ppm of CO2
> pH of 5.8 with 47.6 ppm of CO2
> pH of 6.2 with 18.9 ppm of CO2


This was the beginning of the discussion to try another known drop checker dKH that would work for his tank and indicate a green color for him.



Squawkbert said:


> pH is not an exponential function, it's logarithmic. pH=-log[H+]


I did not mention anything about the formula for pH.

I was talking about the formula used in Chuck's Chart. It's exponential. Here's his formula: The formula used for this calculation is: 
CO2 (in PPM) = 3 * KH * 10( 7-pH ) where KH is Carbonate Hardness in degrees. http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm
Here is what I said and again I believe that you didn't read it clearly:


Left C said:


> The formula is exponential (it's based on 10 to the -7 power). This means that the concentration of CO2 varies very little with small pH changes at the higher KH values. It's the exact opposite for lower KH values. The CO2 concentration varies tremendously with small pH changes. You can easily see this when you look at Chuck's graph. http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm


 Notice that I didn't mention anything about how to measure pH.

The exponential function is a different way of explaining the logarithmic function and vice versa.

This is from wikipedia:
"The exponential function is one of the most important functions in mathematics. It is written as exp(x) or ex, where e equals approximately 2.71828183 and is the base of the natural logarithm.
http://en.wikipedia.org/wiki/Exponential_function

In mathematics, a logarithm of a number x in base b is a number n such that x = bn, where the value b must be neither 0 nor a root of 1. 
A good way of remembering is by asking: "b to what power  equals x?". In other words, it is the exponent or power to which a base must be raised to yield a given number.
http://en.wikipedia.org/wiki/Logarithmic_function"



Squawkbert said:


> The beauty of the drop checker is that you isolate your 4dKH standard solution in the checker. The aquarium water pH, dKH etc. just does *not *matter at all.
> 
> When the gasses dissolved in the tank water reach equilibrium w/ the air in the drop checker, the checker will tell you how much CO2 is in the water as a function of the change in pH *within *the drop checker. 4dKH water has a pH a little over 7. Adding 15-30ppm CO2 to the system drops the pH to 7 (or a hair lower - enough to make the solution green). If you want the thing to go green at a higher level of CO2, you increase the dKH *inside *the checker. This raises the starting pH a little more so more CO2 is required to drive it back to green. As long as you make a good standard carbonate solution, you will have a highly accurate, reproducible reading.
> 
> ...


Thanks for going over this but it's been discussed many, many times over the past few months. I'm glad that hoppy came up with it.

I appreciate your help but I believe that you may of misread some of the things that were being discussed.


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## goalcreas (Nov 20, 2006)

I also now realize that my reagent might be breaking down from the light, I was not aware that that was a factor.

I had posted a question in my Arizona forum about how in one tank that thru the week, it gets more light green to yellow. Was that because of built up CO2, or because the PH was gradually going down thru the week? Nobody gave ma a good answer, but the light breaking down the reagent seems to fit.

The other tank, the ph is low and the reagent, when fresh immediatly turns yellow once in ther for about 20 minutes. My thoughts as I wrote in the begining of the thread is because the PH is low and the drop checker is essentially checking PH that I can't get a read in this tank.

That tank is newley set up and the fresh substrate is probably part of the reason that the KH and GH and PH are low anyways, so in the future when it settles down and is Fish ready, I don't see it being the same problem.

Of coures, these are my theories and any flaws you can point out to me in this logic will be noted and appreciated. Left C has been doing a splendid job in giving me insight so far as well as most who have posted in this thread so far.
Although it is not my thread to begin with, I think that this has turned out to be a pretty good thread afterall, Even if it has been discussed many times over, some of those threads get buried and with busy, hectic schedules, who has time to go digging them up, right?


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## ed seeley (Dec 1, 2006)

As far as I understand it the pH of the tank water shouldn't effect how the drop checker works so i'm a bit confused as to why your's seems to stay yellow with no CO2.

The drop checker works by reaching an equilibrium of CO2 levels in the tank water with the 4dKH water in the drop checker. The CO2 present in the aquarium water comes out of solution into the air space in the drop checker then dissolves into the water in the drop checker. This will reach an equilibrium so the CO2 levels in both otherwise isolated bits of water will be the same. This process is why it takes some time for the colour to change. (I'm sure you know all this, but I'm trying to explain why I'm confused that the pH of aquarium water makes a difference for you.)

With the right reagent (which I'm wondering might be the problem??) a 4dKH solution should be a nice green colour when the CO2 level is 30ppm, regardless of the tank pH. My main tank has a pH of 5.5 (caused by 0dKH of the water and the peat in the filter as well as the pressurised CO2) but the drop checker works fine.


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## goalcreas (Nov 20, 2006)

Well It is an Red Sea Drop Checker with their Reagent.
That is the only one I have ever used, but I just got in last night from Aquatic Magic some of the glass drop checkers with new Reagent. I do have the 4dkh solution that I got from Billionz (sp?).
I will do some more testing as with work and being so busy right now, it was more of throw it in there and think about it, not test it.


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*

Hi Guys

I'm a little confused right now on a few issues. Let me run this past you guys and find out what you think about these comments.

It makes perfect sense that a 4 dkH reference solution in a drop checker would be completely independent of what's in the tank. A green color would indicate ~ 30 ppm CO2 when the solution in the drop checker reaches a pH of 6.6.

I have AP's freshwater pH color card that I'm looking at. Do you guys have one of these to look at? Their pH indicator solution is Bromothymol blue. Bromothymol blue's transition pH range is from 6.0-7.6. That's the same scale as on the AP color card.

The card indicates basically the same green color from a pH 6.4 to 7.0 on the color card. A pH of 7.2 and higher is clearly some shade of a blue color. On the lower pH end of the card. It shows that a pH of 6.0 is yellow.

Let me spell this out in a list form that may make more sense if you don't have this pH color card to look at. I am also going to list the CO2 levels beside the various pH levels and colors that comes from Chuck's calculator using a 4 dKH reference solution.

The AP pH freshwater color card shows:
pH 6.0 - yellow - 120.0 ppm CO2
pH 6.4 - green - 47.8 ppm CO2
pH 6.6 - green - 30.1 ppm CO2
pH 6.8 - green - 19.0 ppm CO2
pH 7.0 - green - 12.0 ppm CO2
pH 7.2 - aqua blue - 7.6 ppm CO2
pH 7.6 - mariner blue - 7.4 ppm CO2

This is telling me that a green color according to this color card shows a CO2 concentration from 12.0 to 47.8 ppm. It's hard to distinguish an exact CO2 level of 30 ppm. It just shows a safe range of CO2 levels if the color is either green or blue. A green color is what we want when the lights are on. If the color is yellow (and the Bromothymol blue solution is fresh) you may have a disaster.

I don't know if I was right or wrong about using a 1 dKH reference solution and trying to get it to indicate a green color when the solution inside the drop checker becomes a pH of 6.0. That calculates out to a CO2 concentration of 30 ppm. I'm not sure if I was taking into account how the Bromothymol blue solution actually works.

"Bromothymol blue is a chemical indicator for weak acids and bases. The chemical is also used for observing photosynthetic activities or respiratory indicators (turns yellow as CO2 is added).

Bromothymol Blue acts as a weak acid in solution and therefore can be in acid or base forms which appear yellow and blue respectively. It is green in neutral solution."

What do you guys think?

References:
Chuck's calculator: http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

Wikibedia - Bromothymol Blue: http://en.wikipedia.org/wiki/Bromthymol_blue

PS: This comes from the same Wikibedia reference. Do you want to freak some people out?
"Ingesting BTB (Bromothymol Blue) will color urine brightly blue for a day and will also color stomach content similarly."

Left C 
__________________


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## epicfish (Sep 11, 2006)

http://fins.actwin.com/aquatic-plants/month.9602/msg00091.html

I'm too tired to make sense of anything right now with the math, but I'll do it later today. Anyone else want to try in the meantime?


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*

Thanks, epicfish. You may not need to do the math. I understand the math part just fine.

My question really centers around what is Bromothymol Blue's color at various pH levels and a CO2 concentration of roughly 30 ppm inside the drop checker by using various reference dKH solutions.

I've made a little chart that I used Chuck's calculator to get the numbers. In my previous post I was using AP's pH color card to go by to get the color scheme of Bromothymol Blue. I was saying that according to this color card that a pH from 6.4 to a pH of 7.0 is a greenish color. Somewhere between ~ 7.0 and 7.2; Bromothymol Blue goes from a greenish color to a bluish color. On the other end on the pH scale, the Bromothymol Blue goes from a greenish color to a yellow color somewhere below at pH of 6.4. It is yellow at a pH of 6.0.

My previous post used a constant reference dKH of 4 and I was showing how the concentration of CO2 changes from a pH of 6.0 to 7.6.

The following chart shows the pH level needed to keep the CO2 concentration faily constant at 30 ppm + or - 0.3 ppm by increasing reference dKH levels one whole integer at a time from 1 to 16. Then I'm going to use the AP's pH indicator for the color reference.

*pH* --- *KH* ---*CO2 30ppm +/- 0.3ppm* - *Bromothymol Blue Color*
6.00 - - 1 - - - - - 30.0 - - - - - - - - - - - - - - - yellow
6.30 - - 2 - - - - - 30.1 - - - - - - - - - - - - - - - yellowish green
6.48 - - 3 - - - - - 29.8 - - - - - - - - - - - - - - - green
6.60 - - 4 - - - - - 30.1 - - - - - - - - - - - - - - - green
6.70 - - 5 - - - - - 29.9 - - - - - - - - - - - - - - - green
6.78 - - 6 - - - - - 29.9 - - - - - - - - - - - - - - - green
6.85 - - 7 - - - - - 29.7 - - - - - - - - - - - - - - - green 
6.90 - - 8 - - - - - 30.2 - - - - - - - - - - - - - - - green
6.95 - - 9 - - - - - 30.3 - - - - - - - - - - - - - - - green
7.00 - -10 - - - - - 30.0 - - - - - - - - - - - - - - - green
7.04 - -11 - - - - - 30.1 - - - - - - - - - - - - - - - green
7.08 - -12 - - - - - 29.9 - - - - - - - - - - - - - - - greenish blue
7.11 - -13 - - - - - 30.3 - - - - - - - - - - - - - - - greenish blue
7.15 - -14 - - - - - 29.7 - - - - - - - - - - - - - - - blueish green
7.18 - -15 - - - - - 29.7 - - - - - - - - - - - - - - - blueish green
7.20 - -16 - - - - - 30.3 - - - - - - - - - - - - - - - blue

Does this chart help to explain things or does it cause more confusion?


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## Squawkbert (Jan 3, 2007)

*Re: CO2 drop checker*

Left C - You may well be right - I may have misread some or not gone back far enough to get the full picture. I was just trying to make sure that we were making proper distinctions about where the standard solution was to be located etc.

That said, I will assert that drop checkers @ 4dKH will go yellow somewhere between 30ppm CO2 and fish death (>>100ppm). The charts appear to be correct in that green covers a nice safe range that most plants like (but that's a pretty big gap in the one chart, going from 30 to 120).

The drop checker that's showing yellow w/o any CO2 being in the water - we have a problem there. Something (acidic) must have contaminated that one, maybe a little Si sealant during assembly over at RedSea or the reagent is just shot (I had one go pretty much yellow on me when it got old, others just faded).


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*

Everything's fine Squawkbert. I appreciate your help. I know I skim articles too.

There was something wrong that was making his solution to be a gold color. I have the Red Sea indicators.The directions say this: "Note the CO2 Indicator will give incorrect readings if the °KH drops below 4°." I don't know why Red Sea says that unless indicator solution is not very good.

I was asking goalcreas about trying a low dKH solution to help with his problem. I just tossed the question "up in the air" so to speak. I really wasn't sure if it would work or not. I did the math but I didn't take into account how Bromothymol Blue works. I dug a little deeper and it seems that a broad range of known (or reference) dKH solutions will show a green color but Bromothymol Blue's color indicating properties are pH dependent. So, trying a low dKH of 1 won't work for our purposes as near as I can tell.

Those two little charts that I did more or less proved that a low dKH won't work, I think. The first chart that I did kept the dKH (4°) the same and I increased the pH and calculated the CO2 level. Then I used the AP pH color card as an reference to see what the color may be. The second chart, I kept the CO2 level fairly constant (30 ± 0.3 ppm). Then I increased the dKH one unit at a time and calculated what the pH level would be at these increasing dKH values while keeping the the CO2 level close to 30 ppm. Then I got my "trusty" pH color card out and compared it to what I just did. Again, it proved that a low dKH won't work for our use. I was wrong in my assumption, I do believe.

These results are generated by using math and using a color card that is probably not very accurate because of the color variation that can occur when the color card was printed. These results were not tested in a lab. It is just conjecture.

I know that Hoppy was wanting to come up with color standards to indicate what the differing shades of green were indicating. He was wanting to tell more exactly what the CO2 level actually was. I understand what he was trying to do because was a colorist for many years. I don't know how far he got with this.

The bottom line (IMO) is that whether we use Chuck's calculator to figure our CO2 levels or we use a drop checker; we still don't know exactly what the precise CO2 level actually is. Chuck's calculator can be skewed by the various chemicals in the aquariums and the accuracy of the test kits. The drop checker can be skewed by the differing shades of green that is indicated. But, the drop checker is much more accurate and it tells us whether we have a good level of CO2 or too much or too little CO2.

Even though Bromothymol Blue has a narrow pH range from 6.0 to 7.6; I just wish that there was a little better CO2 sensitive indicator than Bromothymol Blue. Some type of "Specific Indicator" that would be able to indicate a color change range a little sharper than Bromothymol Blue. Some of the wide range pH indicators use a solution that contains a combination of chemicals to indicate the pH. I wish that there was a "reverse wide range" type of indicator that works over a very short range with sharp color changes. Something like the color indicating solution in Lamotte's alkalinity test kits would be great. There is a sharp contrast there. You can easily tell if you have too little, too much or it's just right.


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## Left C (Jun 14, 2005)

*Re: CO2 drop checker*



Squawkbert said:


> ...The charts appear to be correct in that green covers a nice safe range that most plants like (but that's a pretty big gap in the one chart, going from 30 to 120)...


The 120 ppm is yellow and not green. The numbers came from using Chuck's calculator. It's expotential, you know.

I didn't calculate the CO2 level for a pH of 6.2 because it's not on the AP color card. At a KH of 4° and a pH of 6.2; the CO2 level is 75.7 ppm (probably the "dead zone").

The AP pH freshwater color card shows:
pH 6.0 - yellow - 120.0 ppm CO2--<--<--<--"dead zone"
pH 6.4 - green - 47.8 ppm CO2
pH 6.6 - green - 30.1 ppm CO2
pH 6.8 - green - 19.0 ppm CO2
pH 7.0 - green - 12.0 ppm CO2
pH 7.2 - aqua blue - 7.6 ppm CO2
pH 7.6 - mariner blue - 7.4 ppm CO2

So the chart shows green from 12.0 to 47.8 ppm. This is based on looking at AP's color card. I don't think that it's very precise but it's close.


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## dirtmonkey (Mar 12, 2007)

Stepping off to the side a moment...

Left C wrote:


> PS: This comes from the same Wikibedia reference. Do you want to freak some people out?
> "Ingesting BTB (Bromothymol Blue) will color urine brightly blue for a day ..."


It works. It's invisible in black coffee. Ask my HS science teacher *hehehe*. There was punishment involved though, he knew exactly what happened. Probably happened every year.

No, I didn't do it, but I knew about it *snicker*


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## Left C (Jun 14, 2005)

That's a hoot, dirtmonkey! :ranger: ...  ... :badgrin: ... :angel:


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## Newt (Apr 1, 2004)

Left C and/or Squawkbert,
Could you explain (again) why one would use 5 dKH solution vs 4 dKH solution and vice versa?


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## Left C (Jun 14, 2005)

5 dKH requires more CO2 to turn the BB solution the same shade of green as 4 dKH would. 3 dKH requires less CO2 than the 4 dKH would to turn the same shade of green. It's a way to "tune" your drop checker.


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## Newt (Apr 1, 2004)

So if my pH is ~6.6 to 6.4 and a drop checker with 4 dKH and one with 5 dKH are green then the 4 dKH would be ~ 30 ppm and what would the 5 dKH drop checker indicate for a CO2 concentration? This is the point I'm missing.


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## wet (Nov 24, 2008)

Newt said:


> So if my pH is ~6.6 to 6.4 and a drop checker with 4 dKH and one with 5 dKH are green then the 4 dKH would be ~ 30 ppm and what would the 5 dKH drop checker indicate for a CO2 concentration?


38ppm CO2.

You folks will like this calculator.
http://wet.biggiantnerds.com/drop_calc.pl

Maybe you can get a more accurate idea of CO2? Follow all the linkage starting here. 
http://www.aquaticplantcentral.com/...-reference-kh-target-co2-calculator-drop.html


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## Left C (Jun 14, 2005)

Newt said:


> So if my pH is ~6.6 to 6.4 and a drop checker with 4 dKH and one with 5 dKH are green then the 4 dKH would be ~ 30 ppm and what would the 5 dKH drop checker indicate for a CO2 concentration? This is the point I'm missing.


http://csd.net/~cgadd/aqua/art_plant_co2chart.htm

Take a look at the chart in Chuck's article above, 4 dKH and pH 6.6 is 30 ppm of CO2. This is what we are calling "green" even though the BB solution is some shade of green over a wider range.

In order to get this same "green" color with 5 dKH, you will need a pH of 6.7.

So, higher KH requires more CO2 than a solution with a lower KH. And, vice versa.

SuMo sells 15 ppm, 30 ppm and 45 ppm drop checker solutions. These have differing KH measurements. Let's go to Chuck's chart again and look at a pH of 6.6 only. Now let's find where 15, 30 and 45 ppm occur. You see that these are at 2, 4 and 6 dKH.

pH 6.6 - 2 dKH - 15 ppm CO2
pH 6.6 - 4 dKH - 30 ppm CO2
pH 6.6 - 6 dKH - 45 ppm CO2

Using differing dKH solutions allows you to "tune" your DC to a certain CO2 level depending on your needs. For most of us, 4 dKH/30 ppm solutions are fine.


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## Newt (Apr 1, 2004)

I've got it now.
Thanks


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## Newt (Apr 1, 2004)

I have drop checkers for my 75gal planted and 10gal shrimp tank and recently got some drop checker solution.
Is it possible to add too much of the Bromothymol Blue? 
I am adding 11 drops to 5 mls of 4dKH and the blue is easy to see but becomes very light when it turns green and under the tank lights. 
So could I add more to make the color darker without altering the reading?

BTW, I get the same reading when using tank water and the color shows up better when green.


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## wet (Nov 24, 2008)

20 drops is about 1mL, so if you use enough of the reagent you'll find the KH of the mix will drop, making the green CO2 range less than what you're expecting. But remember: ball park is good enough unless you want to nerd it up, and drop checkers (or the two drop checker idea) just makes a smaller ballpark. Tried placing the drop checker near a clean corner and used a white background on the outside of the glass? View the drop checker from the uncovered side, of course.


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## Newt (Apr 1, 2004)

I figured a little more would just take longer to turn color and too much would make the solution opaque and no longer transparent.

I was reading a thread where Left C recommended white finger nail polish opposite the viewing side. I was going to try that.


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## wet (Nov 24, 2008)

Left C is smart. I like his idea better -- let's you move around the drop checker to ensure good CO2.


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## Newt (Apr 1, 2004)

Yup. Left C has posted a lot of great information. Especially on fert/dosing info - great, useful stuff.


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## Left C (Jun 14, 2005)

Thanks guys. LOL









When you paint one side, they are now left handed or right handed DC's then.

The Red Sea and Cal Aqua Labs "Oracle" DC's have white centers so that you can read the color easier and they aren't left or right handed.


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## Newt (Apr 1, 2004)

Left C can you comment on my post above. (#42 permalink)
thanks


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## Left C (Jun 14, 2005)

I think wet summed it up very well.


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## Left C (Jun 14, 2005)

API's Bromothymol Blue Freshwater pH Color Card shows a light green color at a pH of 6.6. It is quite a bit lighter in color than the darker blue color at the endpoint pH of 7.6. As we know, a pH of 6.6 with a 4dKH carbonate based solution indicates 30 ppm of CO2. The light green color is somewhat "the nature of the beast."


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## bosmahe1 (May 14, 2005)

Left C said:


> API's Bromothymol Blue Freshwater pH Color Card shows a light green color at a pH of 6.6. It is quite a bit lighter in color than the darker blue color at the endpoint pH of 7.6. As we know, a pH of 6.6 with a 4dKH carbonate based solution indicates 30 ppm of CO2. The light green color is somewhat "the nature of the beast."


Looking at the card, a ph of 6.4 is the color that probably corresponds to "it's too light and I can't see what color it is". So, if it looks clear, it may mean it's at 48 ppm CO2 concentration.


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## Newt (Apr 1, 2004)

I cut back on the injection time and the color is more like 6.6.

Thanks all:fish2:


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