Sand filters, also called high-rate sand filters, were once the most common type but now have been eclipsed by cartridge filters (see Swimming Pool Filters: Cartridge).

Sand filters are larger than both cartridge and diatomaceous earth filters (see Swimming Pool Filters: Diatomaceous Earth) because they must hold 200 or more pounds of sand. They are the least effective type of filter, removing particles only as small as 25 microns or so (as compared to 3 microns for a DE filter and 5 microns for a cartridge filter). Still, if you already have a sand filter, it will do a sufficient job of keeping your pool clean.

The tank, which may be metal or plastic, is pressurized. Water enters near the top, is forcefully sprayed down through the sand, and exits near the bottom. The sand traps the particles.

The main drawback is the heavy maintenance schedule: A sand filter must be washed once a week or so. To wash it, you must reverse the flow of water to “backwash” the sand. In doing so, you will waste about 500 gallons of water.