### Calcium and Magnesium Hardness

Water hardness can be classified based on metal ion namely calcium hardness and magnesium hardness. Most of natural water has calcium and magnesium hardness due to calcium and magnesium ions. Calcium and magnesium hardness often need to be known to determine amount of lime and soda ash which is needed in the process of water softening (lime-soda ash softening). If the calcium hardness value is known so magnesium hardness can be determined through the following equation:

Magnesium hardness = Total Hardness - Calcium hardness

In determining hardness value of total hardness, calcium hardness and magnesium hardness, the presence of iron and manganese are considered as nuisance because it can react with the reagent which is used. Therefore, calcium hardness is assumed greater than the level of calcium ions, and vice versa. The following equation can be used to get the level of calcium ions and magnesium ions of hardness value:

Levels of Ca2+ (mg/liter) = 0.4 x calcium hardness
Levels of Mg2+ (mg /liter) = 0.243 x magnesium hardness