# Testing for CO2 concentrations



## Gizmo (Dec 6, 2010)

I'm running a pressurized CO2 system on my 30 gallon, heavily planted and heavily populated. I've been using the algorithm relating KH and pH to estimate the CO2 concentration in my tank, but I've heard that is very inaccurate. However, I've found it to be more than sufficient.

My question is this: Aside from a drop checker, what other methods are there to test for CO2 concentrations? Also, what is a drop checker exactly?

The algorithm I have been using is this:

CO2 (in ppm) = 3*KH*10^(7-pH) (KH in degrees)
KH(degrees) = 0.056 * KH(ppm)

Reference:
Aquarium CO2 Calculator

And I use no phosphates or buffers, nor do I treat my tank water aside from fertilizers for my plants and tap water dechlorinator during PWC's.
:angler_fish:


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## James0816 (Jun 19, 2009)

Drop Checker. Throw everything else out the window. Using a true 4dKH solution and a couple drops of pH reagent, you will be able to monitor your CO2 level much easier.


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## jrman83 (Jul 9, 2010)

Some use the method of testing Ph......waiting 24hrs and testing again. Requires you to remove a cupful of water and doing both test from the cup of water. If the different is one full point your ppm is 30, .5 15ppm, etc.


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## Gizmo (Dec 6, 2010)

James0816 said:


> Drop Checker. Throw everything else out the window. Using a true 4dKH solution and a couple drops of pH reagent, you will be able to monitor your CO2 level much easier.


So what is a drop checker? How does it function? How do you test with it?


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## James0816 (Jun 19, 2009)

A drop checker is a device that measures the amount of CO2 in the aquarium. Here's an example of one: 

Drop Checker

I actually have a couple of these.

As the CO2 diffuses through the air in the DC (Drop Checker), it will react with the pH reagent in their which will cause it to change color. 

When you initially set it up, it should be a nice blue color. Over a period of time, that color should change to either green or yellow.

To break that down:
Green - Perfect. You have the right amount of CO2 being diffused in the tank
Blue - Neutral. You need to add more CO2.
Yellow - High. You have too much CO2. (This basically applies to if you have critters in the tank. If it is a plant only tank, you can get away with it).

Now, when you first get these, the instructions will actually tell you to use tank water. That is a falsey as it will give you an incorrect reading. You want true 4dKH solution. That is just a calculated mix of baking soda and RO/DI water.

Hope this helps.


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## jrman83 (Jul 9, 2010)

I like the green leaf drop checkers. They're all glass.


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