The 3 Types of Pool Filters
🪨 Sand Filter
A sand filter pushes water down through a tank filled with special filter sand (or glass media). Fine particles get trapped in the sand bed as water flows through. When the sand gets loaded with debris, the pressure gauge rises and you backwash — reversing flow to flush the trapped dirt to waste.
How to maintain it: Backwash when the pressure rises 8–10 PSI above the clean baseline. This takes about 2–3 minutes. Run to waste until the sight glass runs clear. Sand needs replacement every 5–7 years as the grains round off and lose trapping ability.
🧻 Cartridge Filter
A cartridge filter uses a pleated polyester element — similar to an HVAC filter — to trap particles. No backwashing required. When the cartridge gets dirty, you remove it, rinse it with a garden hose, and reinstall. It filters finer particles than a sand filter and uses less water since there's no backwash waste.
How to maintain it: Rinse the cartridge monthly during swimming season. Do a deep-clean (soak in filter cleaner solution) once or twice per year to remove oils and mineral buildup. Replace the cartridge every 2–4 years when the pleats become damaged or won't clean up anymore.
⚗️ DE Filter (Diatomaceous Earth)
A DE filter uses grids coated with diatomaceous earth — the fossilized remains of tiny aquatic organisms — as the filter media. It filters particles as small as 2–5 microns, the finest of any pool filter. The tradeoff is more maintenance: you backwash, then re-charge the filter with fresh DE powder through the skimmer.
How to maintain it: Backwash when pressure rises 8–10 PSI above baseline. After backwashing, add 1 lb of DE powder per 10 sq ft of filter area through the skimmer with the pump running. Fully disassemble and inspect the grids annually — cracked grids bypass DE into the pool (you'll see white powder in the water).
Comparison at a Glance
Filter Troubleshooting
High Pressure (8–10+ PSI above baseline)
The filter is dirty. Clean or backwash it. Sand: backwash. Cartridge: rinse or replace. DE: backwash and recharge. If pressure stays high after cleaning, the media may need replacement or the return line may be partially blocked.
Low Pressure (below normal baseline)
Restriction on the suction side — check skimmer baskets, pump basket, and verify all valves are open. Low pressure with weak flow means the pump isn't getting enough water, not that the filter is clogged.
DE Powder Coming Back into the Pool
A cracked or torn DE grid is bypassing powder directly into the pool. Open the filter, inspect every grid, and replace damaged ones. This is not optional — a bad grid means zero filtration on the bypassed section.
Cartridge Not Cleaning Up
Oils and minerals build up in cartridge pleats and can't be rinsed out. Soak the cartridge overnight in a commercial filter cleaner solution. If it still won't clean, replace it — typically every 2–4 years depending on use.
🔧 Having filter pressure issues or flow problems? Describe the symptoms to PoolDiag and get a diagnosis.
Ask PoolDiag →Which Filter Is Right for Your Pool?
Choose sand if: you want the lowest maintenance routine, you're in a region with water restrictions (counterintuitively, sand uses more water per backwash but requires less intervention), or you're replacing an existing sand system.
Choose cartridge if: you want better filtration than sand with no backwash water waste, you're on a well or pay for water by volume, or your pool equipment pad doesn't have a good backwash line.
Choose DE if: you want the absolute clearest water possible, you have a large inground pool with heavy use, or you're willing to learn the annual teardown routine.