what is carbonate hardness
- Carbonate hardness, or carbonate alkalinity is a measure of the alkalinity of water caused by the presence of carbonate (CO2â. 3) and bicarbonate (HCOâ. 3) anions. Carbonate hardness is usually expressed either as parts per million (ppm or mg/L), or in degree KH (dKH) (from the German KarbonathÃ¤rte).