A cartridge filter will filter out 10 to 20 micron particles. The cartridges need to be cleaned out fairly often some as much as every 3 to 4 months depending on the use and debris going into the pool. Whether the filter is correctly sized for the size of the pool will make a difference too.  The cartridges are limited in use and should be replaced when the pleats become loose or the metal bands start to loosen or break. They can last several seasons, but every pool is different and it will depend on the use and maintenance.

SAND FILTERS

A Sand filter will filter out 20 to 100 micron particles and becomes more effective as it captures more dirt. It uses pool grade silica sand as a filter media. The sand needs to be changed out periodically or when the pressure will not lower with backwashing or is 10 psi above the clean reading. While the sand lasts a long time, it can become hardened with calcium, or gummed up with lotions and oils being filtered though the sand. When the sand has deteriorated it needs to be cleaned out and replaced with new sand.