Metal Free™ protects against metal staining. Metal Free™ is a highly effective metal chelating agent that protects against staining and discoloration from trace metals such as iron and copper. Metal Free™ should be used as part of a well designed pool maintenance program. Metal Free™ does not raise phosphate levels in pool water like many other stains and scale products. NOTE: This product can be used with most sanitizing systems and is compatible with all pool surfaces. Do not use with biguanides.