BioGuard Pool Magnet Plus prevents staining due to iron, copper and manganese. It also eliminates discolored water from metals. This product has been recently reformulated and is now more concentrated and effective as ever. Pool experts recommend that this product be used monthly in pools that hold iron-containing fill water. It is only necessary to be used monthly because it stays effective for 3-4 weeks. It is recommended to use Pool Magnet Plus in conjunction with BioGuard Sparkle Up to remove metals from the water.