The Fish Mate Gravity Filter Replacement UV Bulb replaces the old or burnt out UV light in your Fish Mate Gravity Filter. UV bulbs provide an important sterilization agent to keep your tank healthy and clean.Replacement UV bulb for Fish Mate Gravity FiltersHelps keep aquarium water clear and healthyFits Fish Mate 500, 800, 1200, and 2000 Gravity UV+Bio FiltersCarefully follow all Fish Mate directions when installing. It is recommended that waterproof gaskets be replaced when installing/replacing a light.Note: Some models may require two 8 Watt bulbs.