Calcium is a valuable part of balanced water to prevent corrosion of any metal parts and protect pool surfaces. Nuclo Basic Calcium Hardness is 100% Calcium Chloride Dihydrate. It is extremely fast dissolving, pH neutral and is applied directly to the pool or pre-dissolved in water to raise the hardness (calcium) level in your pool to the ideal range. Stops staining and etching of pool surfaces caused by low hardness levels. Great for use in areas where soft water is a problem.