EDTA is most commonly used to determine hardness (i.e., Calcium and Magnesium ions) in water, where the pH must be approximately 10 and is usually controlled by adding a buffer such as Water Hardness Buffer. Water Hardness Indicator (Eriochrome Black T), Eriochrome Blue Black R, Calmagite, and Murexide are used for hardness or Calcium determinations using EDTA.