Abstract: A fluid filter is disclosed which includes a casing defining a fluid chamber with inlet and outlet apertures to and from the chamber to respectively conduct unfiltered fluid to the chamber and filtered fluid from the chamber. A flow path is defined within the chamber and a filter is interposed in the flow path substantially normal to the direction of flow of the fluid in the chamber. The filter includes a screen having a covering of a filter aid, such as diatomaceous earth, on an upstream side of the screen. The filter is regenerated by reciprocating the screen relative to the casing in a path corresponding to the path defined by the direction of flow.