In this guide: When to clean · Sand filters · Cartridge filters · DE filters · Filter size & flow · Calculators
Your filter is the pool's kidney. As it traps debris, resistance rises and flow drops — so the same pump that gave you a full turnover in the spring quietly falls behind by mid-summer if the filter is dirty. The trigger to clean is pressure, not the calendar.
Note the pressure gauge reading right after a clean — that's your baseline. Clean the filter when the gauge climbs 8–10 psi above baseline. Cleaning sooner wastes water and actually reduces filtration (a slightly dirty filter filters finer than a spotless one); waiting too long starves circulation.
With the pump off, set the multiport valve to Backwash, then run the pump ~2 minutes until the sight glass runs clear. Turn off, switch to Rinse, run ~30 seconds to resettle the bed, then return to Filter. Backwashing sends water to waste, so factor that into fill costs. Replace the sand every 5–7 years as the grains round off and stop grabbing fine particles.
Cartridges don't backwash. Turn off the pump, release the air-relief valve, remove the cartridge, and hose it top-to-bottom between the pleats. For oils and sunscreen build-up, soak overnight in a filter cleaner (a degreaser), then rinse. Keeping a spare cartridge lets you swap and clean at leisure. Cartridges use no backwash water — a real advantage where water is expensive.
DE filters backwash like sand but then need fresh DE powder recharged through the skimmer to re-coat the grids — follow the manufacturer's scoop count for your filter's square footage. Once or twice a season, open the filter and hose the grids clean. DE filters the finest of the three, which is why they clear stubborn haze so well.
Each media type is rated for a maximum flow per square foot of filter area (roughly 15–20 GPM/ft² for sand, 1–2 for cartridge, ~2 for DE under NSF/ANSI 50 listings). If your pump moves more water than the filter is rated for, water pushes through too fast to filter well. Use the filter calculator to check that your filter area matches the flow your turnover needs.
These calculators turn the steps above into your exact numbers:
This guide is built on published health codes, national standards, and government energy guidance. For the exact equations behind the linked calculators, see our formula reference.
This guide is general information, not a substitute for your local health code or a licensed professional. Always follow the dosing instructions on your chemical labels and confirm readings with a test kit.