Fluval 2 Fliter Cartridge Multi-Phase & Liqufied Waste Removal System.Easy to use replacement filter cartridges, 3 in a pack. Art. # A-343Installation:Cartridge should be changed when duo-density material becomes clogged or discoloured by debris. Inspect cartridge regularly. Change cartridge every two weeks if necessary. Dirty or heavily loaded aquarium communities will require cartridge replacement more often.RRP: £3.99