A salt water pool requires regular maintenance to function properly. Part of the maintenance program includes a filter to clean the pool of debris. You can use either sand filters or filters with washable cartridges. A clean sand filter catches particles as small as 40 microns. Backwash the filter regularly to clean the sand. The sand will gradually degrade and eventually will not be an acceptable filter medium. At this point you must replace the sand.
Clean Sand Regularly to Extend Life
Wash out the filter sand at least monthly. Shut off the pool motor and turn the multiport valve to the "backwash" setting. Open the air bleeder and use a garden hose to run water through the filter until it comes out clear. The sand will last longer if it's kept clean.
Replace Sand When It Is Exhausted
At the end of its useful life, the filter sand will clump together and form channels. This happens every 7 to 10 years with normal use. Open the drain plug and remove the top dome of filter. Remove all the old sand with a scoop, vacuum cleaner, and garden hose. Fill the filter 3/4 full of new sand and immediately backwash it twice.