GLB 71212A Pool Calcium Hardness Up, 15-Pound Increase water hardness to prevent foaming, equipment corrosion and scaling with calcium hardness up Helps to maintain proper calcium hardness level of 150-250 ppm 1-Pound of calcium hardness up will increase the calcium hardness 10 ppm in 10,000 gallons of pool water Properly balanced water will prevent the formation of scale deposits and eliminate the corrosion of metal pipes and fixtures Compatible with chlorine, bromine, ozone, salt water pools and biguanide sanitizers