PRO Series® Stain & Scale Control™ 20705PRO 5 gal Pail. Pro Series Stain & Scale Control protects pools from the damaging effects of scale buildup and staining due to excessive calcium, iron, copper and other minerals. It works without the use of phosphates or harsh acids. This product also works very well at preventing/reducing scale from forming on chlorine generator cells and UV crystal lens in order to help maintain optimum performance. Pro Series Stain & Scale Control can be used with most sanitizing systems (do not use with biguanides) and is compatible with all pool surfaces.