Metalfree Protects Against Metal Staining. Metalfree is a highly effective metal chelating agent that protects against staining and discoloration from trace metals such as iron and copper. Metalfree should be used as part of a well designed pool maintenance program. Metalfree does not raise phosphate levels in pool water like many other stain 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.