GLB Pool & Spa Products 71212 15-Pound Calcium Hardness Up Pool Water Balancer Determine calcium hardness level; it should be between 150-250 ppm If level is below 150 ppm, add calcium hardness up by distributing product over the water surface Properly balanced water will prevent the formation of scale deposits and eliminate the corrosion of metal pipes and fixtures Compatible with chlorine and salt water pools, and biguanide sanitizers; 1-pound of quantity will increase the calcium hardness 10 ppm Measures 11.5-inches in length by 9.9-inches in width by 6.5-inches in height