Best way to measure CO2 concentration

[Sonny Disposition]

After talking with Sean during the microfishing trip yesterday, it occurred to me that I might have a better idea of what the CO2 levels are in my Walstad style planted tank during the different parts of the lighting cycle.

What's the easiest, most accurate way to measure levels of dissolved CO2 in the water? I did a search on "Aquarium CO2 test kit." and a lot of different options turned up, and I'm not really sure which one I'm looking for.

Thanks.

[JLW]

I've never heard of an accurate CO2 test kit.

Use a meter to measure your pH, and then measure your dKH. There are charts that'll give you the concentration from there.

[tug]

Ultimately, you want your CO2 levels to stay the same throughout the lighting period, which should be about 2-3 ppm in your case. This is done by providing sufficient water flow across the water's surface to allow for ambient CO2 levels to remain steady. HOB filters are also good for the same reason as well as they help remove surface film.

The other way to maintain consistent CO2 levels is performing fewer water changes and why weekly water changes are a bad idea for tanks that don't add CO2. Plants spend a lot of energy building the enzymes they need to take in lower levels of CO2, when the levels of CO2 increase, the plant stops building and even repurposes those enzymes until the CO2 levels are low again when the plants have to start over rebuilding. Algae do not do this, so fluctuating CO2 levels are to their advantage.

I agree with Joshua. CO2 would be difficult to test at the levels in your tank. If your KH is all from carbonates the CO2/pH/KH table would give you a ruff idea but there are a host of things that can effect pH once it's in our tanks, other then CO2. Honestly I'm note sure how easy it is to get an accurate KH reading. I'm not sure I could, were I to try.