Replace a pool filter cartridge about every 3 years. That’s Pentair’s average for its cartridges under normal conditions, and heavy use, wind and dust shorten it.
Replace sand when the top of the bed has gone hard and crusty. Replace a DE grid when it has a tear or hole. The surest sign it’s time for any media: cleaning no longer brings the pressure gauge back to its clean reading.
Use your pressure gauge as the test
Write down the pressure with clean media. That’s your baseline. (Not sure which filter type you have? See sand vs cartridge vs DE filters.) The manuals give these cleaning points:
| Filter (manual) | Clean or backwash when pressure rises |
|---|---|
| Pentair Clean and Clear RP cartridge | 8–10 psi above starting pressure |
| Pentair System 3 sand | 10 psi above the initial reading |
| Hayward ProSeries sand | 6–8 psi above the initial reading |
| Pentair FNS Plus DE | 10–12 psi above starting pressure |
The replacement signal is what happens after cleaning. Pentair’s DE manual says that if starting pressure after cleaning reads 4 to 5 psi higher than normal, the elements must be given a full cleaning. Example: your clean baseline is 12 psi, so you clean at 20–22 psi. If the gauge reads 17 psi right after cleaning, the media is holding dirt that washing no longer removes. Deep-clean once; if the baseline still doesn’t come back, replace.
Cartridges
- Plan on about 3 years (Pentair’s average), sooner with heavy bather loads, wind or dust.
- Replace now if the fabric is torn, the end caps are cracked or loose, or the pleats are flattened.
- Between replacements, clean at 8–10 psi over baseline; see how to clean a cartridge filter.
Sand
- Inspect the bed at least once a year, as Pentair’s System 3 manual says.
- Replace all the sand when the bed gets hard and crusty on top.
- Sand in the pool is not a sand problem. Pentair says sand in the pool means a broken lateral; fix the lateral, or fresh sand will come straight back. See sand coming back into the pool.
- Use the sand grade and quantity on your filter’s label.
Short runs between backwashes have other causes too; check the backwashing guide before blaming the sand.
DE grids
- Inspect the elements for any tears or holes whenever you take the grids out, and check the internal air bleed sock too.
- Replace a grid that is torn, or that stays stiff and coated after a full cleaning.
- DE powder is not a replacement part. You add fresh powder after every backwash or cleaning.
Before you open any filter
Turn the pump off at the breaker so it can’t restart. Then open the air release valve and release all pressure from the system before loosening a clamp or lid. Never operate the filter above 50 psi. If the tank, clamp or lid is cracked, stop and replace that part first. For pressure readings that don’t make sense, see pool filter pressure too high or low.
Sources
- Pentair: Clean and Clear RP Cartridge Filter User’s Guide
- Pentair: System 3 Sand Filter Owner’s Manual
- Hayward: ProSeries sand filter owner’s manual (IS210S1S)
- Pentair: FNS Plus Vertical Grid D.E. Filter Installation and User’s Guide
Research checked 2026-10-08.
