How often should you replace a pool filter cartridge?
Updated July 2026
Replace a pool filter cartridge every 1–3 years, once the pleats break down and the pressure no longer drops even after a thorough cleaning. Year-round pools closer to 1 year, seasonal ones closer to 3. The clue is the gauge: if a fresh deep-soak no longer brings the pressure back to baseline, the media is spent, not dirty, and no amount of rinsing revives it once the pleats stop trapping debris.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Cleaned on schedule, standard use | Every 1–3 years | The media slowly breaks down with each cleaning |
| Year-round or warm-climate pool | Closer to 1 year | More run time wears the pleats faster |
| Pressure high right after cleaning | Replace now | The media is spent, not just dirty |
| Pleats frayed, flat, or torn | Replace now | Damaged media cannot filter properly |
| Small spa cartridge | About yearly | Less area means it works harder |
| Running a two-cartridge rotation | Extends each set | Drying between uses adds life |
The cost of skipping it
What skipping it costs: a worn cartridge lets fine debris pass straight back into the pool, so the water stays hazy no matter how often you clean the filter or how balanced the chemistry is. You burn through clarifier and shock chasing a problem the cartridge itself is causing, and poor filtration invites an algae bloom. A fresh cartridge is $20–120 depending on size, and it clears the haze in about a day.
How to do it (15 minutes · DIY)
- Shut off the pump and release the trapped air with the filter housing's relief valve before you open it.
- Open the housing, lift out the old cartridge, and inspect the pleats: frayed, flattened, or torn media will not filter no matter how clean it looks.
- Match the replacement by the part number molded into the end cap, or by measuring length, diameter, and end-cap style.
- Lubricate the housing o-ring with a silicone (never petroleum) lube, seat the new cartridge, and close it up.
- Restart the pump, bleed the air, and note the fresh clean-pressure reading as your new baseline.
Knowing the interval is the easy half. OnOtto reminds you at the right interval, and it won't let you snooze it into next year. Tasks persist until they're done, and completing cartridge replacements schedules the next one automatically.
Put this on autopilot, free for 30 daysFrequently asked questions
How do I know the cartridge is worn out versus just dirty?
Dirty cleans up: a soak or a backwash drops the pressure back to baseline. Worn out does not. If the pressure stays high right after a thorough deep-clean, or the pleats are frayed, permanently flattened, cracked at the end caps, or torn, the media is spent and no amount of rinsing brings it back. That is the line between cleaning the filter and replacing the cartridge.
Can I make a cartridge last longer?
Yes, within limits. Rinse it on schedule, deep-soak it in filter cleaner a few times a season, and rotate two cartridges so each dries fully between uses. Good chemistry helps too: balanced water and controlled scale keep the pleats from clogging with calcium. These habits push a cartridge toward the 3-year end of its life, but once the pleated media physically breaks down, no amount of care revives it.
Are generic replacement cartridges as good as OEM?
Quality generics that match the exact filter area and micron rating usually perform fine for less money; the risk is cheap ones with less media, flimsy end caps, or thin pleats that clog and fail early. Match the model number and check the listed square footage of filter area against the original. A cartridge a size too small filters worse, works harder, and wears out well before its time.
How do I find the right replacement size?
The easiest route is the part number molded into the plastic end cap; search that and you will get exact matches. No number? Measure the length, the outside diameter, and the end-cap style (open hole, closed, or a molded handle), and match all three. Filter-cartridge cross-reference charts line up the common Pleatco, Unicel, and Filbur equivalents that fit the same housing.