Calcium Hardness Plus is a highly refined, calcium-rich mineral designed to increase hardness levels in spa water. A clean white granule, this product is used when calcium levels are low to increase them. This prevents premature deterioration of tub surfaces, including synthetics and vinyl, as well as unnecessary corrosion of equipment and metal surfaces. Calcium hardness also plays an important role in ensuring that the overall mineral balance is correct, improving comfort, chemical effectiveness and cost of maintenance.