A sand filter for use with swimming pools includes a tank that has a hollow interior space and a top diffuser for allowing spent pool water to enter the tank and for distributing the pool water inside the tank. The sand filter also includes filter media formed as a bed of material on a bottom of the tank and also includes laterals that are located under the filter media and allow filtered pool water to exit the tank and flow back to the pool. The filter media includes a bed of sand that is disposed on the bottom of the tank and a layer of perlite material that is disposed on a top surface of the bed of sand. The perlite material is a high flow rate, low density perlite material that only contains a trace amount of floaters.