The Velda Internal Venturi Filter is a trouble free filter system for your pond. It filters & aerates your pond water at the same time. With the help of the snorkel the built in pond pump sucks in a constant supply of oxygen to feed the friendly bacteria that clean the pond. The Venturi comes equipped with all of the necessary filter materials & the built in pump aeration hose & snorkel can all be simply connected. The Venturi filter cleans the pond in 2 biological stages: In the first stage the visible dirt particles are removed by the filter foam. In the second stage the growth of micro-organisms is stimulated with the help of the ‘ Filtra-Sub’. These micro-organisms remove organic elements from the pond water. In both stages the activity of the filter material is optimum due to the constant oxygen supply resulting in clear & healthy pond water. to read more information on the Velda Venturi Filter.