Spa Stain & Scale™ controls calcium buildup & metal staining. It protects spas 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. Spa Stain & Scale™ also works to prevent scale from forming on salt generator cells to help maintain optimum performance. NOTE: This product can be used with most sanitizing systems and is compatible with all spa surfaces. Do NOT use with biguanides.