WHAT IS CARBONATE HARDNESS?
The extent of carbonate and bicarbonate contained in a sample of water is the Carbonate Hardness value of that sample. Carbonate Hardness affects all aquaria, both salt and fresh. It is called many names, according to the jargon of an industry or country of origin of the test kit, eg CARBONATE HARDNESS = ALKALINITY = kH (German) = ACID BINDING CAPACITY.

STABILITY OF pH
The Carbonate Hardness of water is an important measurement, because the level of Carbonate Hardness is the basis for the value of the pH in a given sample of water. A strong Carbonate Hardness reserve in water can mean a very stable pH and the bonus of an alternative supply of carbon dioxide for plants and algae if supply runs short in an aquarium. This applies equally for marine or freshwater aquaria.