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DIY Drop Checker

273202 Views 357 Replies 80 Participants Last post by  HeyPK
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:
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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,
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)

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

Thanks again,
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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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?
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.
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?
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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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?
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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Thanks for taking the time to get that out Hoppy, I appreciate it!
Yeah Hoppy, thanks! That is what I was fishing for in my last post. Wantplants asked in a better way than I.

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

- Joe
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 \\:D/ .

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 \\:D/ .

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.
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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