Calcium hardness defines how hard or soft your pool water and it’s measured by the dissolved calcium. Water that contains little or no calcium is called soft and water that contain high levels of calcium is considered hard. The ideal range for plastered pools is 200ppm-400ppm. Pools that have high calcium harness level may see white film/crusty deposits, reduced circulation and cloudy water. Too little can cause corrosive water which etches plaster, pits concrete, dissolves grout, and pits pool decks. You can increase your hardness level with calcium chloride. To decrease the hardness level, add fresh water that has lower calcium hardness levels.