Abstract: A diatomite filter device for cleansing fluid carrying particulate matter in the micron size range comprises a filter housing having top and bottom plates and a manifold beneath the latter. A supply conduit communicates with the manifold and with a valve-controlled diatomite reservoir. Flexible tubular filter bags in the housing have inlet openings at the bottom and are mounted about flanges adjacent inlet openings in the housing bottom plate, the latter being in communication with the manifold for a supply of fluid. Each bag has an interior skeletal frame for preventing bag collapse during a backwash operation and an exterior wire mesh skeletal frame for preventing ballooning of the bag during the filter operation. The assemblies comprising a bag and its two associated skeletal frames are mounted at lower end portions about their flanges by means of clamping rings and, preferably, each flange has a horizontal flange at the top notched to receive lower end portions of the inner skeletal frame.