DescriptionIncrease Calcium for hot tubs boosts the natural hardness of spa water. This prevents excessive etching and corrosion of hot tub equipment caused by water which contains very low levels of dissolved calcium. Also reduces foaming caused by soft water. Fast-dissolving form for spas Increases low calcium level Prevents corrosion & foaming Product notes: Contains granular calcium chloride, 100%. 1 oz. of this product added to 500 gallons will increase calcium hardness about 10 ppm. Test with Hardness Test Strips.