Calcium hardness tablets are used in the testing of calcium hardness levels present in swimming pools. Pool manufacturers sell them for consumer and industrial use. Most change the color of pool water as an indicator of how much calcium is currently present in the water. The calcium salts react with the presence of ethylenediaminetetraacetic acid (EDTA). Calcium hardness tablets are also used in water systems like steam raising plants and boilers. The testing is done in an alkaline solution in a handheld container to keep out any magnesium salts that might interfere with the test. Most testing is done using a 50 mL sample. A larger one may be used when a lower testing range is needed. The tablets should be added one by one and shaken in the solution. All tablets should be dissolved entirely before making a final assessment of calcium hardness levels present in the body of water.