Backwash
Also called: backwashing, backwash and rinse.
Backwashing cleans a sand or DE pool filter by reversing the flow to flush the trapped dirt out to waste. Backwash when the pressure gauge reads about 8 to 10 PSI above the filter's clean baseline, never on a calendar. A cartridge filter does not backwash at all.
Why it matters
Do not backwash early. A sand bed traps finer particles as it loads, so a slightly dirty sand filter filters better than a freshly backwashed one. An early backwash costs the water down the drain, the balanced and stabilized chemistry that goes with it, and a return to coarser filtration. Always rinse afterwards, or the disturbed bed sends dirty water straight back at the pool. On a DE filter every backwash flushes the powder out with the dirt, so every backwash ends with a fresh charge of DE. Never move the multiport valve with the pump running.
In numbers
The sand routine: pump off, valve to BACKWASH, pump on, run until the sight glass runs clear, usually two to three minutes, then RINSE for about 30 seconds before returning to FILTER.