Hagen's Fluval 4 Filter Cartridge 3/pk Multi-phase and liquified waste removal system. Duo-density polyester layer. Firmly traps solid particles. Evenly loads with debris for long life. Prevents waste flow back during media change. Carbon impregnated layer. Uses only highest quality powdered coconut carbons. Powdered carbons provide more absorptive surface area. Actively absorbs liquid impurities |