# Does it work? ADA glass dropcheck co2 indicator



## newguy

Drop Checker

does this thing work?


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## Gomer

I can't see why not. Toss some bromothymol blue into DI water and let CO2 reach equalibrium in the trapped air pocket. walah. No real magic there...just a nice piece of glassware for it to happen in.


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## newguy

Gomer said:


> Toss some bromothymol blue into DI water and let CO2 reach equalibrium in the trapped air pocket. walah. No real magic there


that sounded like magic to me  looks like it's out of stock on adg, would it work if i buy the adg liquid and use it in some other dropchecker made by redsea?


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## Gomer

newguy said:


> that sounded like magic to me  looks like it's out of stock on adg, would it work if i buy the adg liquid and use it in some other dropchecker made by redsea?


99.9% sure that they work on the same principle...just would need the Red Sea CO2 color scale if it is a different indicator. And there really is no reason the indicator would need re-filling unless you spill it.


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## Salt

From what I understand, it's nothing more than a pH indicator.


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## Gomer

Salt, yup! ADA looks to use bromothymol blue but I am not sure what RedSea uses.


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## newguy

Curious, if this works and is accurate why dont everyone use them? Wouldnt it be very very helpful to have constant co2 monitoring? Even if it's just low, normal, or high indicator?


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## turtlehead

Cause some people already know if their co2 is set at the right levels. Some don't want more equipment in the tank. This is not a necessity in my opinion if yout plants are doing great.


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## hoppycalif

I was very interested in using one of these until I realized just how hard it is to measure pH accurately using a test kit with a color chart to match the color to. This complicates that color matching because the color is now in the water in the tank. Then I found that the KH/pH method, which this is, can say I have 30 ppm, when I only have 5 ppm, or it can say I have 120 ppm, when I have less than 30 ppm. So, I gave up the idea.


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## newguy

hoppycalif said:


> I was very interested in using one of these until I realized just how hard it is to measure pH accurately using a test kit with a color chart to match the color to. This complicates that color matching because the color is now in the water in the tank. Then I found that the KH/pH method, which this is, can say I have 30 ppm, when I only have 5 ppm, or it can say I have 120 ppm, when I have less than 30 ppm. So, I gave up the idea.


so basically it doesnt work? now i am confused.


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## Bert H

I understand what Hoppy's saying. Basically, it can be quite difficult to match a particular shade of a color to a color chart when you're holding a test tube in one hand and the chart in another. Now imagine that tube being inside a tank full of water, etc. 

Secondly, the accuracy of that particular test (the kh/pH relationship) has been shown to be quite variable depending on the presence of any other acids in your tank. Many folks have thought they had much higher or lower amounts of CO2 than what was in actuality due to these errors.

Thirdly, the method is accurate in the sense that it is based on a simple acid/base colorimetry reaction where a pH indicator will change colors depending on the pH present. 

Clear as mud now? 

Personally, I prefer the degassed tank water measurement followed by increasing the gas and observing your fish.


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## Gomer

> Secondly, the accuracy of that particular test (the kh/pH relationship) has been shown to be quite variable depending on the presence of any other acids in your tank. Many folks have thought they had much higher or lower amounts of CO2 than what was in actuality due to these errors.


This doesn't matter one bit. The indicator is disolved in DI/RO/Nanopure water. The GH and KH is zero. Since the color change is purely a gas phase equilibrium, what you see is what you get. Bromothymol blue is blue at pH 7.6 and yellow at pH 6.


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## Bert H

> This doesn't matter one bit. The indicator is disolved in DI/RO/Nanopure water. The GH and KH is zero. Since the color change is purely a gas phase equilibrium, what you see is what you get.


I didn't realize that Tony. Thanks for clearing it up.


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## newguy

from adg, looks pretty easy to tell


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## hoppycalif

Gomer said:


> This doesn't matter one bit. The indicator is disolved in DI/RO/Nanopure water. The GH and KH is zero. Since the color change is purely a gas phase equilibrium, what you see is what you get. Bromothymol blue is blue at pH 7.6 and yellow at pH 6.


So, this test takes the tank water out of the equation? Does this mean it assumes that the CO2 in the tank water and in the indicator device is the same in ppm, by having the CO2 being measured come from the tank water? I'm not a chemist, so I don't know much about this - does this truly remove the variables in our tank water from the picture? If so, I will certainly buy one of these. My eyes work pretty well for judging yellow-green-blue, so it would work pretty well for me.

Now, what ppm of CO2 does ADG consider to be ideal? And, is the color change sensitive enough to judge "ideal" + 10 ppm as bein different from "ideal" minus 10 ppm? Since these seem to still be out of stock we have time to explore these questions before sinking the $38 + shipping in one.


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## Steven_Chong

I bought one these things this summer.

And here's my reasoning:

-I'm in Japan, and it's here in front of me for $20.
-It's sexy

There you go.  lol (I'm an idiot, yeah??) :jaw: 

Anyway, it's as the pictures show. I run an air stone at night, so the indicator's usually a dark green in the morning, and at the "just right" yellow color by the time I come back from class. I'm not so good with sophisticated tests so this is a good tool for my level of intelligence I think.  

Is it necessary? Not at all. XD

Is it sexy? Yes!! <33

Anyway, I have one, it's useful, and I seem to be getting the CO2 my plants need to them. That's all.


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## hoppycalif

This has aroused a lot of interest for me. The idea that the indicator/water solution would not be tank water was very intriguing since that would seem to get around the acidity/alkalinity variations in tank water that are not associated with CO2. So, I emailed Jeff Senske at ADG. I asked:


> I am very interested in this method for measuring how much CO2 is in
> my aquarium. So, I have a few questions:
> 1. On APC this was discussed and it was said that this uses pure
> water, with no KH, plus the reagent in the bulb, leading me to
> believe that the CO2 indication is independent of the contaminants of
> various kinds in the aquarium water. This would eliminate the effect
> of alkaline substances or acid substances in the water. Is this true?
> 2. Does the color chart with the unit tell you the pH or the ppm of
> CO2? The information on the website leads me to believe that all it
> does is indicate "acceptable" if the solution color is greenish. If
> so, what ppm of CO2 does that indicate and with what accuracy?
> 3. How often do you have to replace the indicator solution?
> 4. When will they be back in stock?
> Thanks in advance for any information you can provide on this very
> intriguing new device.


As I expected, I got a quick, informative answer back this morning:



> 1. Actually you fill it with aquarium water.
> 
> 2. It tells you pH. There's no ppm indicated and the "accuracy" is more in
> terms of telling you that you should add more or use less CO2. It's based on
> a simple idea of acidity vs. alkalinity and the need for slightly more or
> slightly less CO2.
> 
> 3. I will have to check to see how often the reagent is replaced. I have
> never personally used it for more than an initial test to confirm the CO2
> supply in a newly set-up tank. It is not something I use routinely.
> 
> 4. ADA is currently out of stock on the Drop Checker. I tried to order a few
> last week. I do not know for sure when they will have more. Likely in the
> month or so.
> 
> You're welcome. It's not really a new device, though. These types of
> checkers and this one from ADA in particular have been around for many
> years.


So, for me it is back to the drawing board. This is just a very elegant form of the in-tank pH testers that are available from other manufacturers at much less cost, but also much less esthetic appeal. But, no more dependable.


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## newguy

> 1. Actually you fill it with aquarium water.


:doh:

thanks for confirming hoppy.


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## werner

There are knock-offs of this available on eBay here


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## hoppycalif

Now that price is low enough to give this serious consideration, but no color standard card is included. The only way I see to use this is to independently determine that you have adequate CO2, and try to keep whatever color that gave as the right color. It does look pretty good though.


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## Gomer

hoppycalif said:


> Now that price is low enough to give this serious consideration, but no color standard card is included. The only way I see to use this is to independently determine that you have adequate CO2, and try to keep whatever color that gave as the right color. It does look pretty good though.


Just use Bromothymol blue and use the 3 images above. Exact CO2 levels aren't important. Getting addiquate CO2 is.


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## hoppycalif

The images don't tell you what is an adequate level of CO2. They tell you what the pH is. If you have low KH, as I do, the pH needs to be lower for adequate CO2 than it was when I had much higher KH. So, the color would be different for the two cases. Where can I get Bromothymol blue? I just bought one of the ebay devices - the cost is low enough just to play with.

Why wouldn't this device work equally well if you loaded it with distilled water with a tiny bit of baking soda to get some carbonate in it? Then, wouldn't the CO2 ppm in the device be the same as in the tank water? And, with "ideal" water, of known KH, the pH would truly represent the ppm of CO2 in both the device and the water. I don't see the flaw in doing this.


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## Bert H

Perhaps I am being a little dense here, but aren't you still measuring the pH? You still have all the factors which affect the accuracy/inaccuracy of this methodology. So you will have a ball park figure with it. Isn't that what you have now just by measuring pH?


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## hoppycalif

Bert H said:


> Perhaps I am being a little dense here, but aren't you still measuring the pH? You still have all the factors which affect the accuracy/inaccuracy of this methodology. So you will have a ball park figure with it. Isn't that what you have now just by measuring pH?


You would be measuring a single pH and not two pH's and subtracting them, which can double the error in their measurement. The downside would be that the color of the reagent would be harder to see, since it would be much farther from the color comparison chart. Also, the water whose pH you would be measuring would have a known KH, with no other sources of alkalinity or acidity except the CO2, which would be the same ppm (?) as in the tank water. So, this should give a much more accurate indication of how much CO2 you have, without running into one of those cases where your KH/pH say you have 100 ppm CO2 but the fish are perfectly happy. My chemistry knowledge is skimpy, so I am just assuming that these indicators work because the water in the indicator reaches an equillibrium with the tank water so both have the same ppm of CO2. In any case, I have ordered the ebay version of the "drop checker" and will do some experimenting when I get it.


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## hoppycalif

I got my ebay version of the ADA Drop Checker today, eBay: Type1 Co2 Drop Checker-monitoring proper dosage of CO2 (item 250036844403 end time Oct-14-06 06:06:32 PDT), and it's in the tank now. I like it! Here's how it works as a CO2 indicator:

First, take some distilled water, mix in a bit of baking soda, measure the KH, and adjust slowly until you get KH of 4 degrees, as close as you can get it. I used 4 times the normal water sample, so each drop of my AP test kit would equal 1/4 degree of KH. I think I got it to within +/-.1 degree of being exactly 4. Now, this water has no other substance that affects alkalinity and no substance that affects acidity in it, so it is "perfect" water for the KH/pH tables to give the CO2 ppm.

I had previously tested my AP pH kit to see if the number of drops of reagent was critical for measureing pH, and found that it isn't at all critical, just as I would expect. This means you can add more reagent to get a more intense color.

If you check the ph/KH charts, or better yet, the calculator, for KH of 4 degrees, Measuring CO2 levels in a Planted Tank, you see that the pH target to have 30 ppm of CO2 is 6.6. And, an error of .1 in pH gives a range of 25-40 ppm of CO2, which is a reasonable range, since you can actually see the difference between pH of 6.5 and 6.7, so you can easily reduce that error range if you wish, with a good careful look at the color.

Now look at the color chart for the AP or any similar test kit, you see that the color corresponding to a pH of 6.5 to 6.7 is green - slightly yellowish for 6.5 and slightly bluish for 6.7. So, it is easy to judge the color as being green, not blue green and not yellow green.

So, water with KH=4.0 will definitely be green at the pH that gives the correct ppm of CO2 for our tanks. And, if the color is yellowish, the pH will be low enough that the ppm will be much too high - about 70-80 ppm. Likewise, if the color is blueish, the ppm will be much too low - about 10 ppm.

So, if we put this KH = 4 water in the bulb of the "Drop Checker" with enough indicator solution to get a strong color, which took about 7 drops for me, we have not a pH indicator, but a good CO2 indicator.

That's what I did. Getting the water and indicator into the bulb is difficult, because the throat of the "Drop Checker" is small and the air trapped in the bulb will easily stop water from flowing into the bulb. I had to use a syringe with a bent needle to squirt the water into the bulb, the use it again to remove a bit when I had too much in there. I had blue water in the bulb.

I stuck it to the tank wall, about 3 inches below the water line, where I could see the bulb easily, and watched it. After one hour, the color was slightly greenish blue. In another 15 minutes it was blue green. Then I had to go do some political activism and when I got back it was 3.5 hours after I stuck it in the tank. Oops, it was yellow, very yellow! About 3/4 of the fish were at the surface, so I shut off the CO2, and adjusted the needle valve to slightly reduce the bubble rate for tomorrow.

My conclusion is that this works very well to monitor CO2 level in the tank, with a time constant of around 2 to 3 hours - the time to reach approximately the final reading. This is fine for my use. I will keep watching this, and adjusting my CO2 bubble rate accordingly, and will report back in a few days.


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## Laith

Thanks for the results of this experiment Hoppy.

If I understand how this works; CO2 off-gassing from the aquarium water is diffusing into your RO+KH+reagent water sample, the concept being that at one point it reaches equilibrium between the three?

I'm just wondering how accurate a measure that is of the CO2 dissolved in the tank water? Wouldn't there be some distortion due to the fact that it is measuring an amount of CO2 after it has diffused into an air medium and then back into a liquid? Or does the fact that it reaches equilibrium negate any distortion?

Just curious... though it would probably still be more accurate than the standard KH/pH/CO2 tables.


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## onemyndseye

Great run down Hoppy.... you seem like a really sharp cat  You should add this to the APC review archive 

I THINK in my very limited knowledge of chemistry that once that equilibrium is reached that the levels would all equal out (though maybe to some degree of variance) ... even the air portion of the Drop Tester would reach equilibrium with the CO2 levels in the tank. If CO2 and O2 were NOT independant of each other is were I would think the big problems would come into play.... *shrug*

-Justin
One Mynds Eye


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## Bert H

Nice follow-up Hoppy. :thumbsup: Sounds like this is indeed, more accurate than other methods which we have tried. Any chance you can post some pics of the system 'at work', so to speak.


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## hoppycalif

I will try to post a photo of the "drop checker" at work today. Unfortunately I am not educated in the fields that would let me theoretically prove that this does or does not work. My understanding is that the air/water system reaches an equillibrium - no net CO2 transfer from one to the other, and two such systems, connected by the air gap are all in equillibrium with each other, thus the ppm of CO2 is the same in both batches of water. I am passing this by Tom Barr on his website just to get a very critical look at it - and he doesn't think it will work. I hope someone here has the background to offer criticism or comments on it too. Most things that seem too good to be true are.......not true! But, I'm hoping this one is true.


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## freshreef

Gomer said:


> Just use Bromothymol blue and use the 3 images above.


i have found only bromothymol blue powder. how do u make stock solution?


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## hoppycalif

There are only a few indicators used in pH test kits. The one that covers the 6.0 to 7.2 range is bromothymol blue, and that is what the AP test kit uses. I suspect most of the test kits we can buy use it.


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## hoppycalif

Here is the "drop checker" in action in the front corner of my tank. (Notice my ongoing scientific experiment with GDA - entered into solely in the interest of science.)


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## hoppycalif

Tom Barr has just agreed that this idea works! After a bit of disagreement over whether the KH in the "drop checker" bubble would be changed by the tank water, he conceded that would not be a problem. So, I think we have a new winner in the "most accurate way to guess how much CO2 is in your water in one easy step" contest. The little devices are still on sale on ebay too, for anyone wanting to try one, or the ADA original device should eventually be in stock, at a higher price, but probably with better quality.


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## newguy

thanks hoppy for the excellent followups! i guess the only thing remaining is to see how well it works long term. For example after two weeks would the indicator remain balanced, how about after a water change? would it recover etc.


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## hoppycalif

newguy said:


> thanks hoppy for the excellent followups! i guess the only thing remaining is to see how well it works long term. For example after two weeks would the indicator remain balanced, how about after a water change? would it recover etc.


The proof is always in the long haul, but I don't anticipate any problem other than fading or chemical change of the indicator. Water changes wont affect it, since the water in the bulb is totally isolated from and different from the tank water. Like all testing, it becomes less and less important as the tank gets balanced, you know you have the CO2 running right, etc. But, it should be a good alarm for something drastically dropping or raising the CO2 bubble rate. And, the ebay one is pretty cheap.

This morning the indicator color is still green, to my surprise. I may need to readjust my water circulation so it moves the surface water more, and drops the nighttime ppm of CO2.


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## freshreef

mor b said:


> i have found only bromothymol blue powder. how do u make stock solution?


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## freshreef

i have the drop checker , just need fluid


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## hoppycalif

BROMOTHYMOL BLUE SOLUTION
This indicates that you mix bromothymol blue crystals into distilled water, about 1% to 99% water. Apparently it isn't very soluble in water, so mixing might be a problem. You only use this stuff a few drops at a time, so why not just experiment with mixing a bit in distilled water, the adding drops to a known alkaline solution and to a known acid solution to be sure it is blue for alkaline and yellow for acid. As best I can determne, it makes no difference how much you put in as an indicator - all it affects is how intense the color is. You could even use it in the crystal form instead of as drops. It is a bit hazardous though, so don't treat it like table salt.

edit: I just found this:
Bromothymol Blue (BTB)
Bromothymol blue is an indicator, a substance that changes color as the pH of a solution changes. Bromothymol blue is yellow in acidic solutions and blue in basic solutions.

* BTB can be prepared by mixing 0.1 g (a pinch) of bromothymol blue powder in 10 mL of a 4% solution of sodium hydroxide.
* Add 20 mL of alcohol and dilute to 1 L with distilled water.
* The solution should be deep blue.
* If it is green, add sodium hydroxide solution drop by drop until the solution turns blue.
* Bromothymol blue can be purchased from scientific supply houses.

CAUTION: Sodium hydroxide is corrosive; the BTB solution should be prepared in a laboratory. BTB stains hands and clothes. Have students wear goggles and follow safety precautions when using BTB solution.


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## epicfish

Well, here's the science to back up the product.

Background first:
Partial Pressure of a Gas in a Liquid Gases such as CO2, O2 and N2 that are in physical solution in a liquid such as plasma, continually escape from the liquid into the gas phase and may also return to the liquid. When the rate of a gas coming out of solution is equal to the rate at which it enters the solution, the system is in equilibrium for that gas and liquid. At equilibrium, the partial pressure of a gas in gas phase is equal to the partial pressure (or tension) of the gas in liquid.

This is how the solution changes color upon it's FIRST equilibration:
Dissolved CO2 in the water will "reverse" itself to enter the small air pocket in the swan-neck of the dropcheck device. As CO2 begins to revert to it's gaseous form into the air pocket, the concentration of the dissolved CO2 in the water is still higher than that in the air pocket, so the diffusion process continues.

However, as the concentration of the CO2 in the air pocket compared to the concentration of CO2 in the indicator solution (which is 0 right now) increases, the CO2 begins to dissolve in the indicator solution, thus changing it's color.

Basically, the process is dissolved CO2 -> gaseous CO2 in the air pocket -> dissolved CO2 in the indicator solution. Any changes in the concentration of the CO2 will either cause a forward or backwards equilibration reaction.

The biggest drawback to this is the delayed response of the solution to the CO2 levels. Diffusion and dissolution rates of the CO2 depends on many factors: water temperature, air pocket temperature, atmospheric pressure, water circulation around the indicator device, and last but not least, how long the indicator solution has been sitting in the bulb. Since the solution is bromothymol blue sitting in sodium hydroxide (NaOH), be real careful of it. Do not over-fill the bulb. Even though it's a real dilute solution, better safe than sorry.

The MSDS here says the indicator solution should be relatively stable. MSDS :: Bromothymol Blue 0.04% w/v Aqueous, however, if the water temperature is in the higher range, condensation in the air pocket could drip into the indicator solution, thus changing it's concentration, and possibly it's accuracy. This isn't very likely though, because the entire apparatus will be at the same tank water temperature.


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## Original Kuhli

*condensation*

Condensation is only possible if there's a delta/difference in the temperature of the glass to the aquarium water.

This should only be the case on initial installation, so as long as you put warm solution into the drop checker there should be no possibility of modifying the drop checker kH via condensation.


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## junco

Nevermind... disregard. I asked a dumb question and then couldn't figure out how to delete it.


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## Squawkbert

To quickly clarify a few pts - 

1) read Hoppy's long post, AFAIK, all is correct

2) no, you don't use tank water in the bulb
3) no, you don't use RO/DI/Distilled in there either, it's 4dKH water (RO/DI & a trace baking soda)

4) add as many drops of a bromothymol blue indicator as is needed - the low range pH test solution in your AP FW Master test kit will work fine.

5) any stable vessel that will trap the indicator solution in the aquarium with an air gap between it and the tank water is fine - although visibility of the test solution is tough if it's too thin a column


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## chizzow

Hi there!

If my tank water is at PH=6.0, should the distilled water+baking soda mixture still be adjusted to a KH= 4?

thanks everyone


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## Muirner

the distilled water and baking soda should have a KH of 4. If they have a KH of 4, then your readings of co2 will show green at 30 ppm.


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## chizzow

Muirner said:


> the distilled water and baking soda should have a KH of 4. If they have a KH of 4, then your readings of co2 will show green at 30 ppm.


Right, so regardless of the ph in the tank, the kh within the dropper should be set at 4!? so basically kh=4 is universal?


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## Yeaulman

According to this one person on ebay, they say use tank water.

http://cgi.ebay.com/Co2-Drop-Checke...9QQihZ015QQcategoryZ66794QQrdZ1QQcmdZViewItem



> Directions
> 
> 1) Turn drop checker upside down and place 5 drops of reagent inside the checker.
> 
> 2) With a pipette (not included) add tank water to drop checker so that it's half full of water.
> 
> 3) Turn drop checker over carefully (without spilling contents) and place inside aquarium so that it is visible.
> 
> 4) Within 1 hour drop checker will display a reading according to your C02 levels. Green is the ideal colour, yellow is too much C02 and blue is too little (adjust C02 output accordingly)
> 
> 5) After each water change, renew reagent in drop checker by following directions above


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## jazzlvr123

i have one and it definitely works great : )


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## Muirner

Yeaulman - That'll do nothing more then test your PH, you do NOT use tank water because that would bring all of the ellements that make the PH/KH graph hard to read back into play. By using a solution of a known KH, and having an air pocket trapped intbetween them, they will reach equaliberium. The CO2 levels transfered from the water trapped in the bell, will be represented by the bulb color. With a KH of 4, and the air bubble trapped in the middle the equaliberium reached will do nothing more then measure the gas (co2) in the aqurarium



ed seeley said:


> Just add the 4dKH solution to the drop checker, add the indicator solution and then turn it over and submerge so the solution can't mix with the tank water. As Muirner said, the CO2 in the water will come out of solution into the air space in the drop checker and will then dissolve into the solution in the drop checker so that the level of CO2 in all three are the same. When this is 30ppm that will turn a 4dKH solution green. The fact that the CO2 has to get out of solution into the air space then back into solution in the drop checker solution means there is a time lag in the colour change.


 That was taken from here http://www.aquaticplantcentral.com/forumapc/aquarium-equipment/38343-co2-drop-check-how.html


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## Yeaulman

Ok so what happens when you run out of pH indicator solution? Can you order refills or just use a standard pH test kit?


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## turbomkt

Use a standard pH test kit and a known KH solution. Billionzzzz (sp?) sells the KH solution.


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## SongCloud

I have 2 different indicators, one is from RedSea and the other 2 are from Azoo. Both state in their directions to use tank water in the units and add the reagent to it. I have done it this way the entire time that I have had them and I have found them both to be very reliable. For the most part, the reagent reacts for anywhere from 1-2 months for me, but I usually like to clean out the indicators every other month or so or else I find they can build up with slime or other stuff. Just adding my 2 cents to the thread.


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## Muirner

Ok, since you have 2 from Azoo, how bout you set up one of each, one with tank water and one with knowen KH solution. I dont get how putting tank water in would make it show you the co2? Do you put tank water in and then keep an air bubble trapped in the horn of the unit? Can you show me your setup? Hopefully tomorow i'll have time to rescape and scrape the glass and i'll take a few pictures of the way i have mine set up.


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## turbomkt

I can see how tank water will give you your pH, which you can couple with KH (not an exact measurement like known KH solution) but I doubt that it's anywhere close to as helpful as the known KH method. Known KH is literally "read the color and know your CO2 level as low, high or just right".


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## Squawkbert

> According to this one person on ebay, they say use tank water...





> Ok so what happens when you run out of pH indicator solution? Can you order refills or just use a standard pH test kit?





> I have 2 different indicators, one is from RedSea and the other 2 are from Azoo. Both state in their directions to use tank water in the units and add the reagent to it. I have done it this way the entire time that I have had them and I have found them both to be very reliable. For the most part, the reagent reacts for anywhere from 1-2 months for me, but I usually like to clean out the indicators every other month or so or else I find they can build up with slime or other stuff. Just adding my 2 cents to the thread. :-D


^^Guys - Read #42 above.^^



> I can see how tank water will give you your pH, which you can couple with KH (not an exact measurement like known KH solution) but I doubt that it's anywhere close to as helpful as the known KH method. Known KH is literally "read the color and know your CO2 level as low, high or just right".


Turbomkt - Right. pH/KH charts are not as accurate because KH is a measure of (just) carbonate hardness. Your tank has sources other than carbonate contributing to hardness, but your test kit for hardness can't discern carbonate hardness from all other possible sources of hardness, so it's not that accurate. Even if it were accurate, all you get is a point in time reading. You can't spot trends without a lot more testing. Drop checkers may be a little behind in terms of time, but where things have been vs. where they're going is quite valuable information (and they're more accurate than charts unless you have aquarium water that is unusually devoid of ion sources).


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## Blacksunshine

Best way is to use a soloution of known kH. using tank water introduces alot of variables to the soloution that won't read in the expected range properly. 
I make ready to go regent as well as Drop checkers. And I've found in my testing of these things that using the known stable soloution is much more accurate and easier then trying to use tank water.


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## Dutch-AquaDesign

Muirner said:


> the distilled water and baking soda should have a KH of 4. If they have a KH of 4, then your readings of co2 will show green at 30 ppm.


I have read this topic with much interest.
But I do have some questions... 

1) Is the KH of 4 depended of my pH
So yes, what will it be for by example a pH of 7

2) How must be the KH when I want 25 ppm in my water?

3) Can someone explain me the calculations?



Squawkbert said:


> .... it's 4dKH water (RO/DI & a trace baking soda).....


4) What are the exact ingrediënt of dKH water?


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## turbomkt

KH depends on your water source.

The goal here is to find a particular KH, that will indicate a particular color with the pH test agent (bromothymol blue). Targets are based on info like this.

4 and 5 dKH solutions give good targets for CO2 levels based on Estimative Index, etc. They are a combination of RO water and a reference solution to create the target of 4 or 5 dKH.


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## Dutch-AquaDesign

On this moment the pH=7 and the dKH=8 of my fish tank water (CO2=24 ppm)
Remark: My dKH is this high because I don't use RO water in my fish tank.

When I understand this well, I still measure the pH value.
And the RO solution with pH reagent has a turning point of color at pH=6.6, no matter what.

So:
I need a RO solution with a dKH=4 to get a CO2=30 ppm, and do I need a RO solution with a dKH=3.6 to get a CO2= 27 ppm, no matter what.

Is this correct?

So the pH value of my fish tank has to drop to pH=6.6 directed by CO2 and will change my dKH automatic to dKH=3.6. Or is there more I need to do to get the right values?

Will this only work at a pH=6.6 or will this also work at an different pH value?
Do I need an other dKH of my RO solution when I have an different pH value?


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## Dutch-AquaDesign

I read a lot about a dKH=4

Is it necessary to use RO water (not pure) in my fish tank?
In my fish tank the dKH=8.

Can I use this test to see my co2 value is right?
Do I need an other dKH value in my tester?


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## Bert H

The drop checker needs kh4 water *NOT* tank water to do its job properly. If you're going to use tank water, you'll still be subjected to the same errors you had when you were just measuring kh/pH from the tank directly.



> Is it necessary to use RO water (not pure) in my fish tank?


No. Unless you want to completely control the kh of your system and/or need softer water to grow the few 'soft water' plants.



> In my fish tank the dKH=8.


Nothing wrong with that.



> Can I use this test to see my co2 value is right?


You can use the drop checker to measure your CO2 values, *IF* you use kh4 water in your drop checker.



> Do I need an other dKH value in my tester?


You need water with kh4 for your drop checker.


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## Dutch-AquaDesign

@ Bert H,

Thanks for your reply.

So, I only need KH=4 water for in the tester.
And also, the KH in my fish tank is about 8 dKH, the tester tells me still the accurate CO2 value. 

Is this right?


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## Bert H

If the water in your drop checker is kh4, you will have an accurate reading of the CO2 in your tank, no matter what the kh of the tank water is.


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## Dutch-AquaDesign

Last night (Europe time) I have read a lot about this tester here on this site.
( http://www.aquaticplantcentral.com/...aquarium-projects/32100-diy-drop-checker.html )

And now I fully understand the concept and working.

Everyone thank you for you help.
And Special thanks for Hoppy

For now, I gona order one on ebay&#8230;&#8230;&#8230;..


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## Dutch-AquaDesign

Can someone tell me, how many grams of Baking Soda I need in one liter or gallon of RO/DI water to get a KH=4


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## xjia

several questions in mind:

1.Distilled water usually has low KH, like 1KH, 2KH...
2.Where can i get distilled water ? can i just boil my water ?

3.Let say i use 5ml water(as test kid says) my KH is 1KH.
so i put 1 drop the colour change from blue to yellow,its KH 1,correct?
Then i put little soda,the yellow colour of the water will dissapear right? 
put 1 drop again(total 2 drops= 2 KH), change to yellow, is it KH 2,correct?

the drops i put in does add up right?


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## mulita

*Very Helpful post to understand*

I found this post in a search for answers about how the drop checker works as I am newbie on the hobbie and I started my aquarium using the Red Sea indicator a month and a half ago, and I figured it out I have a problem understanding the drop checher when I got my GH/KH test kit a week ago to address another problem with one of my plants. I have fairly hard water from my tap ( KH=8 GH=17) and so adjusting CO2 injection using aquarium water as indicated in the manufacturer instructions was not a wise advise now that I read, as to this I've been keeping my water around 60 ppm CO2 instead of 30 ppm as I was working with the drop checker really as a pH indicator and adjusting the system according to it, instead of a CO2 Indicator.

Now that I have understand how it work I have prepared Distelled water with 4 dKH to use in the drop checker as indicated here in this post and others to have a real reading about CO2 level in the tank.

Drop Checker is a really nice and very helpfull realtime monitor for CO2 (Actually couple of hours delay but wah). Manufacturers should be addressing explanation like this in their instructions or at least as a reference for the user to go to the net to understand the use of the indicator and how to work with it as preferred by choice, pH indicator or true Co2 monitor.

Very useful post as reading and reference to go to other post for information on how this work and how to use it.


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## Left C

Dutch-AquaDesign said:


> Can someone tell me, how many grams of Baking Soda I need in one liter or gallon of RO/DI water to get a KH=4


I used billionzz's instructions to make my solution using baking soda. You need 3.60 grams to make a 40 dKH solution that you dilute further down to 4 dKH, 5 dKH, etc.
http://www.aquaticplantcentral.com/...lants-discussions/37077-how-kh-standards.html


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## latte hiatus

My eBay HK knockoff drop checker arrived today, so after setup with 4dKH solution (thanks for the excellent instructions!), I stuck the drop checker into the tank using the included suction cup. Checked two hours later, and the drop checker had fallen to the bottom of the tank - the suction cup failed to stick. The water in the drop checker was clear, so it must have mixed with the aquarium water.

Checking the MSDS for bromothymol blue came up with very little - it seems to be a minor irritant only, but are there any possible adverse effects on the cherry red shrimps and snails in the tank? I used 8 drops of bromothymol blue, and the tank is 70 gallons in capacity.

Will be using a better suction cup in the future, but I'm hoping that I'm not the first dope to have used an inferior suction cup for their drop checker.


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## latte hiatus

An update for future reference:

It's been roughly 40 hours since the incident with the bromothymol blue mixing into the tank water, but none of the inhabitants appear bothered by it. I haven't seen my juvenile red cherry shrimp for almost a full day now, but it's most likely just his usual disappearing act. The bromothymol blue seems to have had very little impact, if at all.


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## Manwithnofish

chizzow said:


> Right, so regardless of the ph in the tank, the kh within the dropper should be set at 4!? so basically kh=4 is universal?


Correct me if I'm wrong (like that won't happen)...but why is the selection of kH=4 critical?

Would a kH=6.0 as your standard work? As long as you KNOW what the standard value of your solution is, wouldn't it work? Or does the color range ONLY work when the kH=4.0?


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## Nevermore

Manwithnofish said:


> Correct me if I'm wrong (like that won't happen)...but why is the selection of kH=4 critical?
> 
> Would a kH=6.0 as your standard work? As long as you KNOW what the standard value of your solution is, wouldn't it work? Or does the color range ONLY work when the kH=4.0?


It works best with kH=4. People do use other values. Here is a very good article that explains it: http://www.barrreport.com/articles/2661-drop-checkers-co2-indicators-why-how.html

HTH


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## jmontee

The reason that 4dkH water is necessary is because it has to do with an equilibrium. Deionized water that has bicarbonate added to it to a concentration of 4dKH is pH 6.6 when it has 30ppm CO2 dissolved in it. This is what makes the solution turn green. As the CO2 changes the pH changes so the color of the solution changes. If you use a 6dkH solution thyen the equilibrium point changes and a pH of 6.6 would need a lot more CO2. If you use a 6dKH soluton and push enough CO2 to make it green then you would have 45ppm CO2 which is just toxic for fish.


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## Nevermore

jmontee said:


> The reason that 4dkH water is necessary is because it has to do with an equilibrium. Deionized water that has bicarbonate added to it to a concentration of 4dKH is pH 6.6 when it has 30ppm CO2 dissolved in it. This is what makes the solution turn green. As the CO2 changes the pH changes so the color of the solution changes. If you use a 6dkH solution thyen the equilibrium point changes and a pH of 6.6 would need a lot more CO2. If you use a 6dKH soluton and push enough CO2 to make it green then you would have 45ppm CO2 which is just toxic for fish.


I'm still understanding it myself. That explanation is very helpful. I'm aware that 5dkH standards are sold.


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## Manwithnofish

jmontee said:


> The reason that 4dkH water is necessary is because it has to do with an equilibrium. Deionized water that has bicarbonate added to it to a concentration of 4dKH is pH 6.6 when it has 30ppm CO2 dissolved in it. This is what makes the solution turn green. As the CO2 changes the pH changes so the color of the solution changes. If you use a 6dkH solution thyen the equilibrium point changes and a pH of 6.6 would need a lot more CO2. If you use a 6dKH soluton and push enough CO2 to make it green then you would have 45ppm CO2 which is just toxic for fish.


That's hitting the nail on the head for me. Thanks.


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## Nevermore

I have ADA's drop checker. Instead of filling the checker with aquarium water as they direct, can I fill it with 4 dKH soln and use their pH indicator soln? Or is there something else in their pH indicator soln besides bromothymol blue that will make that not work?


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