CO₂ calculator
The pH + KH method, without a dropchecker. Enter your last pH and KH readings — get CO₂ in mg/L, with a quick read on whether you're in the green zone.
Manfred · the calm chemist
Manfred trusts two numbers: pH and KH. He back-solves carbonic acid equilibrium and tells you the dissolved CO₂. He doesn't pretend the readings are timestamped or paired — that's your job here.
Enter both pH and KH to see the CO₂ value.
How this works
Carbonate alkalinity (KH) buffers the dissolved CO₂ → carbonic acid → bicarbonate equilibrium. Given pH and KH, the dissolved CO₂ concentration is fixed by that equilibrium. The hobby formula below is valid for pH 6–9 at room temperature.
CO₂ (mg/L) = 12.839 · KH (°dKH) · 10^(6.35 − pH)Caveat: the calculation assumes the only acid in your water is carbonic acid. If you use peat, leaf litter, blackwater extracts, or organic acids from heavy bioload, the result reads higher than the actual CO₂.
In the app, Stormy watches this for you over time.