Backwash when the pressure tells you to.

Usually when the gauge reads 8–10 PSI above clean pressure. That’s the rule for DE filters, and it beats guessing.

Some people try to stick to a calendar schedule—once a week or every two weeks. But that’s not how DE filters work. They fill up at different rates depending on how much you swim, how hot it is, and what’s blowing around outside. A fixed schedule means you’re either wasting water or letting the pressure climb too high, which stresses the pump and hurts filtration.

Check the gauge after you clean the filter (that’s your baseline pressure). Once it climbs about 8-10 PSI, backwash. On a heavy-use week that might be every few days. On a quiet week maybe every two weeks. The gauge is honest; the calendar isn’t.

One more thing: after you backwash, add fresh DE through the skimmer. The filter isn’t doing its job without it.