The nexus 220 is the perfect koi filter for koi ponds up to 18,000 litres 4,000 gallons.the filter works by pumping air through the central 'eazy' filter mechanism located in the middle of its circular structure this dislodges waste, dirt and debris and discharges it out of the filter.once clean simply switch the air supply off and it diverts to assist creation of healthy bacteria in the 'floating bed' that spans the area beyond the eazy.as you may have gathered a good air pump is vital to this filter's success.now we offer the airtech 95 with this filter usual price £299.95 to create the perfect package.note delivery of this product may take longer than usual, please call to discuss.