Backwash when the pressure tells you, not the calendar.

Once a week or once a month? Neither. The only number that matters is the pressure gauge.

Your DE filter has a clean startup pressure (usually around 10-15 psi). When it climbs 8-10 psi above that, it’s time to backwash. That might be every two weeks in summer or every six weeks in spring. Depends on bather load, debris, and how much sun hits the pool.

Backwashing on a fixed schedule wastes water, wastes DE, and doesn’t clean any better. You’re just flushing out good filter media early. Also, if you backwash too often, you never let the DE cake build up properly, and fine particles slip through.

If you really want a rule of thumb: check the gauge weekly. If it’s high, backwash. If it’s not, leave it alone.

Your pool doesn’t care what day it is.