API KH test kit Tests tap water & fresh or saltwater aquariums for carbonate hardness (KH). Can be used to determine the proper dose of pH buffers.
What is Carbonate Hardness (KH)?
Carbonate hardness (KH) helps stabilize pH in the aquarium. An aquarium with a low KH level (50 ppm or less) will tend to be acidic. Aquariums with very low KH are subject to rapid pH shifts, if not monitored carefully.