METALfree is a highly effective metal deactivation agent that prevents staining and discoloration from trace metals such as iron and copper. METALfree also prevents scale build-up due to calcium and other minerals. These trace metals and minerals may already be in the pool water or in the fill water. It should be used as part of a well designed pool maintenance program where local water requires it, or where well water is the pool water source. Note: METALfree does not contain phosphonic acids and will NOT raise phosphate levels in pool water