BioGuard Pool Magnet Plus - 1 Quart BioGuard Pool Magnet Plus - 1 Quart Prevents staining due to iron, copper and manganese Eliminates discolored water from metals 1 Quart per 10,000 gallons of swimming pool water Pool Magnet Plus stays effective in your swimming pool water for 3-4 weeks. Re-application may be needed if fresh fill has iron or copper