KH
°KH - Carbonate Hardness KH - Buffering capacity, temporary or carbonate hardness in the water. Also known as 'total alkalinity' or 'acid-neutralizing capacity' (ANC) in some countries. The ‘K’ in KH comes from the German word 'karbonate'. KH is a measure of bicarbonate (HCO3-) and carbonate (CO32-) ions that act as buffers in the water to prevent the pH dropping or changing sharply (especially at night if you have plants in the aquarium). One degree KH is equal to 17.9 mg/I (ppm) CaCO3. It's also measured in degrees. The degree symbol may be replaced with a d (ie. 2 dKH). ...