Cat Mate Replacement Filter Cartridge for Pet FountainCat Mate Replacement Filter Cartridges are for use with the Cat Mate and Dog Mate pet fountains. The fine filter material catches hair and other debris, keeping your pets water clean and healthy. Replacement filter cartridges For use with Cat Mate and Dog Mate Pet Fountains Catches and removes hair and debris from fountain water It is recommended to change out your pets filter every 4 weeks.