A pond filter comprises a housing having a fluid inlet 12 and a fluid outlet 13 and a chamber 16 within the housing holding a plurality of filter media elements 2 which are disposed in a flow path between the inlet 12 and the outlet 13； agitation members 41 are disposed in the chamber 16 for agitating carried filter media elements in a cleaning process. The filter media elements 2 are preferably compressible open celled foam portions which, under action of the agitation members 41, are free to change location within the chamber 16 and move relative to one another.
