Sand pool filters are constituted of a special grade #20 silica sand that is capable of sieving out contaminants and dust particles in the size range of 20 to 100 microns. The irony is that the sand filters tend to have increased efficiency as they collect more and more dirt. This could be attributed to the increase in density of the sand as more dirt gets collected in it. Just like other filters sand pool filters would not continue performing after a period ad you’ve got to backwash them to restore performance.
When the pool pressure gauge shows a reading of 8-10 lbs over it’s initial reading, it’s time to back wash the sand pool filter.