a system for filtering and treating waste generated or collected in the water of a fish pond . the system includes a pump , pre - filter , piping , a valve assembly , and a filter media container enclosing a plurality of discrete filter media . the filter media are generally hollow , plastic structures with a plurality of external ribs and internal dividing walls having a high surface area - to - volume ratio and can support a high volumetric density of naturally occurring heterotrophic bacteria . the heterotrophic bacteria establish colonies on the internal and external surfaces of the filter media and biologically metabolize waste that is trapped on the media . the bacterial metabolization transforms much of the waste to an aesthetically and biologically neutral form thereby reducing the need for chemical treatment of the pond water . the system includes a backwashing mode to agitate and remove unreacted waste from the system and direct the waste stream out of the system .