HTH Pool Care Hardness Up 4 Lb. Calcium Hardness Increaser

Calcium hardness increaser. Low calcium hardness can cause swimming pool water to be corrosive, resulting in damage to pool surfaces, vinyl linings, and equipment. Raising the calcium hardness levels in your water prevents corrosion of your pool surfaces, including metal and plastic. Great for all pool types, including vinyl-lined pools and salt water systems.