The Hayward Bobby Water Filter is a disposable pool filter that attaches to your garden hose to filter out impurities in your fill water. It prevents pool stains by removing iron from the water when filling the pool. Features: Perfect at start-up, after remodeling, or anytime when refilling the pool This disposable pool filter is made from a mono-filament polyprolene, the same kind of material used to make DE pool filter grids 10" pool water filter filters pools up to 20,000 gallons; 20" pool water filter filters pools up to 40,000 gallons