Calcium Hardness Test Kit - AE212 Product Range: 25-500 mg/l as CaCO3 No of Test: 300 Calcium hardness is caused by the presence of calcium ions in the water. Calcium salts can be readily precipitated from water and high levels of calcium hardness tend to promote scale formation in the water system. Calcium hardness is an important control test in industrial water systems such as boilers and steam raising plants. Our Aquasol AE212 kit tests even high levels of calcium in water.