A low calcium hardness level can cause corrosion of your pool's plumbing and heater as well as stain or etch your pool's surface. When the hardness of your . Learn about pool calcium hardness problems and the ideal range for pools. Calcium hardness must be actively managed—along with pH and total . call for maintaining calcium hardness in the ideal range of 200–400 ppm in pools and . When testing pool water for calcium hardness, what you are really measuring is how soft or hard water your swimming pool water is at any given moment. Feb 18, 2016 - Calcium hardness is something that every hot tub owner should . Hot Tub & Swimming Pool Pre-Filter (Turbo Ion Exchange Pre-Filter) 8,000 .