FishMaths

CO2 calculator (pH and KH)

Test your pH and KH, enter them here, and get an estimate of how much CO2 is in your planted tank.

Many planted tanks aim for 20 to 30 ppm.

Result
0
Enter your numbers

How the math works

CO2 in ppm is about 3 × KH (in dKH) × 10 to the power of (7 minus pH). Flip it around and you can find the pH that matches your target CO2, which is what you watch for when tuning a CO2 system.

How accurate is this?
It assumes carbonate is the only buffer in the water. Driftwood tannins, aquasoil and some additives lower pH on their own and make the reading look higher than it is. A drop checker is a good second opinion.
How much CO2 is too much?
Levels much above 30 to 35 ppm can stress fish. Signs include gasping at the surface. Turn CO2 down and add surface agitation if you see that.
Do I need CO2 injection?
Not for easy plants like anubias, java fern and most mosses. Injection mostly helps fast-growing and carpeting plants.