A simple box filter that is suitable for ponds koi ponds up to 1,500 litres or goldfish ponds up to 3,000 litres.Water enters filter via pond pump (not included).Sprayhead distributes water over foam –> foam sieves out any solids whilst the bacteria on the biomedia cleanse pollutants –> biomedia stimulates growth of healthy bacteria and this clean and healthy water returns to the pond. PLEASE NOTE THIS FILTER DOES NOT HAVE A UVC