The Giant Biofill XL is a large multichamber filter: ideal for koi ponds. The water flows up and down through the removable cassettes with filter materials.• Including 18 Watt UV-C Unit which destroys floating algae and germs.• Including Japanese matting, bio filter balls and all connection pieces.• Internal aeration is optional to add oxygen.• Internal Pond Heater is optional in winter.All Velda filters are also available as complete set with Green Line pond pump, UV-C Unit, hose and all adapters.