A larger version of our popular Little Sister 2000 filter, the Big Sister 3500 is well suited for mid-sized koi ponds. With a larger spraybar and output, the Big Sister is able to handle the higher flow rates larger ponds demand. Constructed of rugged fiberglass, the Big Sister 3500 is built to last a lifetime. The Big Sister 3500’s dual chamber design and standard drain valves make cleaning a snap. Each chamber can be cleaned individually in seconds by shaking the filter media and opening the drain valve. This simple process saves countless hours of cleaning time over a single season!