The Hozelock Ecocel 10000 is a gravity-fed filter recommended for ponds up to 10,000 litres, hose 20-40mm. Water enters the unit via a spray head, which is evenly distributed over a foam sheet. Solid particles in the water are trapped in a foam sheet. Almost solids free, the water passes through plastic biomedia where beneficial bacteria cleanse pollutants. The amount of biomedia contained in the filter increases in direct proportion to the size of the filter/pond to support a greater number of fish. Purified water then passes up an outlet tube and back into the pond. A viewing hatch is incorporated to observe the internal operation of the filter, in particular to see whether any maintenance is needed.