PureWater, cited below, gives this definition of "compensated water hardness" or "CH": A measure of water condition used for determining water softener capacity. It takes into account the amount of iron present in water as well as hardness. To determine compensated hardness, add twice the iron...
Calcium determines the hardness of water. It helps to adjust the pH during the mash, assists in the precipitations of proteins in the boil especially during the hot break, enhances yeast flocculation. Many lagers are made with a very low level of calcium and therefore are not required, but...