Backwash when the pressure says so, not the calendar

The only number that matters is pressure: backwash when the gauge reads 8–10 psi above your clean baseline.

Here’s how that works. After you backwash and rinse, let the pump run and write down the pressure on the gauge. That’s your clean baseline, usually around 10–15 psi depending on your system. From then on, don’t touch the filter until the gauge climbs 8–10 psi above that number. That tells you the sand is holding enough dirt to matter.

The time between backwashes will bounce around. After a storm, a heavy swim day, or a week of pollen, it might be five days. In the off-season, it might be six weeks. A fixed schedule either over-wastes water or lets the filter run clogged. The gauge is the only thing that actually knows.

If your filter doesn’t have a pressure gauge, try to take a reading after