The sand in a pool sand filter (#20 silica sand; 45 – 55 mm) is specially graded to trap particles in the 20 – 100 micron range. As a sand filter collects dirt, its efficiency increases, trapping more dirt. When your pressure gauge shows a reading 8 – 10 lbs. over the clean, start-up reading, it is time to backwash the captured dirt out of the filter.
Sand filters are known to be the lowest maintenance of the three types of pool filters. You may only need to open up the tank every 5 years or so. DE filters require removing the internal grid assembly at least annually to clean them well, and cartridge filters don’t backwash, you remove the cartridge and hose clean every so often, depending on the cartridge filter size. Sand filters are the easiest to operate and maintain.
“They say” that the sand inside a sand filter should be replaced after seven years. Gradual loss of efficiency may be hard to notice. If your sand filter requires frequent backwashing, every week or two, the sand bed may be “mudballed”, or it may be “channeled”. It may also “calcify” with calcium deposits. Other water balance problems may also contribute to pool filter sand deterioration, but a properly sized sand filter could go over 10 years between sand changes.