The baseline
Cartridge filters: four times a year, roughly quarterly. There is no backwash to shed load, so everything the pool catches sits in the pleats until someone pulls the element.
DE filters: two to three times a year. Twice is the floor. Backwashing moves some material out, but it never removes the oils and mineral film that blind grids.
What moves you toward more frequent cleans
Bather load. Sunscreen, body oils, lotions, and hair products go straight to the filter and are what actually clog pleats and grids — far more than dirt.
Trees. Live oaks drop in spring, everything else in fall, and the fine material gets past the baskets and lands in the filter.
Pollen. Cedar and oak pollen season in Central Texas can load a filter in weeks.
Pressure. If your gauge is running 8 to 10 psi above the clean baseline, the schedule is irrelevant — it needs cleaning now.
Salt systems, heavy dust events, nearby construction, and dogs that swim all push the number up.
What a dirty filter actually costs you
Restricted flow means less turnover, which means chlorine cannot reach the whole pool and algae gets a foothold in dead spots.
Your pump works harder against the restriction, which costs electricity and shortens motor life. On variable-speed pumps it quietly cancels out the efficiency you paid for.
Neglected cartridges get replaced in two years instead of lasting five, and DE grids tear when they are cleaned only after they are packed solid.
Why a hose rinse is not a filter clean
A hose knocks off surface debris. It does not remove the oil and mineral layer bound into the pleat fabric or grid cloth, which is what actually restricts flow.
A real service is a teardown, a deep clean, inspection of grids, bands, manifolds, standpipes, and O-rings, correct reassembly, and a recorded clean-pressure baseline you can watch all season.
