GH vs KH — what each one actually does
The two hardness numbers most aquarists use interchangeably, the chemistry that separates them, and why your fish care about one and your pH cares about the other.
General hardness and carbonate hardness sound like the same number measured two ways. They aren't. GH is what your livestock cares about — the calcium and magnesium that build shells and shells and trigger or block breeding. KH is what your pH cares about — the carbonate buffer that holds the daily CO₂ cycle steady.
You can have any combination of the two if you're mixing RO and remineraliser. Most tank problems that get blamed on "hardness" are actually one of these two doing the wrong thing while the other looks fine.
Full prose coming soon. The GH, KH, and hardness converter are already live.
