Carbonate hardness

Carbonate hardness, or carbonate alkalinity is a measure of the alkalinity of water caused by the presence of carbonate (CO2−
3) and bicarbonate (HCO−
3) anions. Carbonate hardness is usually expressed either as parts per million (ppm or mg/L), or in degree KH (dKH) (from the German "Karbonathärte"). One degree KH is equal to 17.848 mg/l (ppm) CaCO
3, e.g. one degree KH corresponds to the carbonate and bicarbonate ions found in a solution of approximately 17.848 milligrams of calcium carbonate (CaCO
3) per litre of water (17.848 ppm). Both measurements (mg/L or KH) are usually expressed as mg/L CaCO
3 – meaning the concentration of carbonate expressed as if calcium carbonate were the sole source of carbonate ions.