Abstract: A filter system using at least two filter vessels with a plurality of filter elements having absolute filtration capability. The filter elements use a nominal filter of diatomaceous earth, or a Perlite filter aid precoat layer, an outer wire layer, an absolute filter layer, a fine wire layer, a coarse wire layer, and a tube core for receiving filter flow therein. A pump is provided for injecting a predetermined amount of filter aid to a precoat tank containing clean fluid. The slurry of filter aid and clean fluid is then pumped into one of the filter vessels for precoating the filtering elements. The unfiltered fluid is then allowed to enter the vessel and be filtered through the filtering elements while virgin filter aid is continuously injected into the unfiltered fluids prior to the fluids entering the filter vessel. One filter vessel is converted to a cleaning mode while the second filter vessel continues filtering in response to a signal in a differential pressure element.