Fluid filter with pleated septum

A diatomaceous earth filter, comprising:

• (a) a hollow housing having a fluid inlet and a fluid outlet;
• (b) a filter septum of flexible, fluid permeable material for supporting a precoat of diatomaceous earth and disposed within said housing for filtering a pressurized stream of fluid entering said fluid inlet, passing through said precoat and said septum and out said fluid outlet, said filter septum being a generally cylindrical, pleated cartridge with a perforated core cylinder;
• and
• (c) a piston axially reciprocable within said core cylinder to simultaneously induce flows out of said perforated core cylinder in areas approached by said piston and into said core cylinder in areas from which said piston retreats when said piston is reciprocated creating a media regenerative flow of fluid within said filter distinct from said flow attributable to said pressurized stream, said media regenerative flow disturbing said precoat on said septum at least in part by bending said flexible septum.