Perfect pond solution for ponds sized up to 15,000 litres (3,300 gallons). By simply twisting a knob on the Fish Mate 15000 filter it automatically cleans itself! In the \'run\' position the water undergoes a 4-stage purification process. Simply turn the knob to \"Clean\" and the foams are squeezed by up to 1000lb of water pressure forcing out pond sludge. The back-flushed dirty water is then pushed out through the second waste outlet (typically down the drain or flowerbeds). The filter also boasts a built-in 13w UVC and guarantees clear water for ponds up to 15,000 litres. (Figures based on pond in full shade with water plants - 7,500 litres for ponds in full sun). The Fish Mate 9000 pond pump supplied is from the same manufacturer, features very low running costs and is highly reliable.