Backwash your sand filter when the pressure gauge tells you to.

There’s no single number. Backwashing on a fixed schedule (weekly, monthly) is wrong more often than it’s right. A clean filter runs at a certain pressure—note that when you install fresh sand or after a deep clean. When the gauge climbs 8-10 PSI above that baseline, it’s time to backwash.

Over-backwashing wastes water and can channel the sand bed, making filtration worse. Under-backwashing means poor flow and cloudy water. The pressure gauge is the only honest judge. Check it every few days during heavy use, but let the numbers decide. And give it a solid 2-3 minute backwash, until the sight glass runs clear, then rinse for 30 seconds.

Your pool’s filter will tell you exactly what it needs—just listen to the gauge.