Cartridge filters:

Turn off the pump. Remove the filter, hose it off, and soak it in detergent according to the manufacturer’s instructions for removing oils. Repeat every three to four months..

Sand filters:

Turn off the pump. Circulate water through the filter in the reverse direction for about 10 minutes, a process known as backwashing. Repeat once per month.

Diatomaceous earth (DE) filters:

Turn off the pump. Backwash the filter (see above), then add more diatomaceous earth to the skimmers. Water will carry the D.E. to the filter and recoat it. Repeat every three to four months.