Cara's Pool School — hardness

Although only slightly different than Calcium Hardness, a Total Hardness test also includes magnesium as part of its reading and should be ideally maintained between 250 - 500 ppm. If Calcium Hardness levels are too low for any real period of time, water can become aggressive toward the pool surface, tile grout, and equipment components exposed to the water; which will result in permanent corrosion and damage that will require repair or replacement. When Calcium or Total Hardness levels get too high, the water can turn cloudy (referred to as precipitation) or deposits (referred to as scale) can form in/on...