Sand filters are one of the most popular ways to filter water. Although they do not filter out particles as small as the D.E. or cartridge filters, they are relatively simple, effective, and require very little attention. Pool water is routed through a sand-filled pressure vessel.
Over time, dirt accumulates in the spaces between the sand particles, causing the pressure in the vessel to rise as water finds it harder to pass through. This signals you to "backwash" the filter. Simply reverse the water flow and "knock out" the dirt.