a formula and method for reducing water hardness includes the combination of a sulfate donor , salt of phosphoric acid , and salt of sulfamic acid . preferred formulas include effective amounts of sodium bisulfate , sodium hexametaphosphate , and sulfamic acid . in a swimming pool , preferred formulas are effective in reducing calcium to under 200 ppm within a two day period . in addition , preferred formulas provide ongoing effectiveness in suppressing scaling , staining and cloudy water .