How is the hardness of water expressed?
This is where things get confusing, because there are several ways of expressing water hardness. Different books, test kit manufacturers and fishkeeping experts use different measures. It’s a grey area – most of the industry experts we spoke to admitted some confusion. Measures of hardness GH – General, total or permanent hardness is a measure of the overall concentration of calcium, magnesium and other ions. It’s measured in degrees, with one degree equal to about 17.9mg/l. The degree symbol is often replaced with a “d” (i.e. 6dGH). The harder the water, the higher the GH. KH – Buffering capacity, temporary or carbonate hardness. The ‘K’ in KH comes from the German word ‘karbonate’. KH is a measure of bicarbonate and carbonate ions that act as buffers to prevent the pH dropping. The ions that make up KH can be removed by boiling. KH makes up a component of GH, so boiling will also reduceGH slightly. One degree KH is equal to 17.9 mg/I CaCO3. It’s also measured in degrees. The degree s
