BioGuard Erase Iron Stain Remover is specifically formulated to combat iron-based stains, restoring your pool surfaces to their former beauty. Its proprietary granular formula can be added directly to pool water over the trouble areas, and is compatible with plaster, tile, and vinyl surfaces to accommodate virtually all pools. It can even be used to remove cobalt staining on fiberglass pools! Best of all, Erase Iron Stain Remover is made by BioGuard, an industry leader for decades, allowing you to buy with confidence.