The Laguna Replacement Bulb, 28 Watts, is the replacement bulb for the Fluval UV Sterilizer/ Clarifier 2000. It is for ponds between 1000-2000 gallons and has a flow rate of 500-1000 GPH. All you have to do to change the bulb is simply twist off the end, remove the prong UV bulb, and replace it with a new one.