How to Replace Pool Filter Cartridges, and When

Replace pool filter cartridges when cleaning them no longer drops the pressure back down, when the pleats are torn or matted flat, or on a schedule of every 1 to 3 years for most backyard pools. A cartridge is the pleated paper element that traps dirt as water passes through your filter. Until it is truly worn out, cleaning usually beats replacing.

Here is how to tell the difference, and how to do the swap without soaking yourself.

How do I know when a cartridge needs replacing?

Watch the pressure gauge on top of the filter. Write down the pressure right after a fresh clean. That is your baseline (clean starting pressure). As dirt builds up, pressure climbs. Once it rises about 8 to 10 PSI above baseline, the filter needs attention.

The key test is what happens after you clean it. If a deep clean brings pressure back to baseline, the cartridge is fine and just needed a bath. If pressure stays stubbornly high even after cleaning, the pleats are permanently clogged and it is time for a new cartridge.

Also replace on sight if you see torn pleats, cracked plastic end caps, a collapsed core, or pleats matted flat instead of standing open. Damaged elements let dirt slip straight through, which cloudier water and more chlorine demand will confirm.

How long do pool filter cartridges actually last?

Most last 1 to 3 years. Heavy use, lots of swimmers, sunscreen, pollen, and poorly balanced water all shorten that. Gentle use and good chemistry stretch it.

Cleaning frequency matters too. A cartridge you rinse and soak on schedule outlives one you run dirty for months. Balanced water helps more than people expect, because scale and residue bake into the pleats when pH and calcium drift high. If your chemistry feels like guesswork, our guide to pool chemistry basics walks through what to test and why.

Salt pools are not exempt. The cell handles chlorine, but the cartridge still catches the same dirt, so the same replacement rules apply. New to a salt system? See saltwater pool maintenance for beginners.

How do I replace a pool filter cartridge step by step?

Take it slow and keep the parts in order. The whole job runs about 20 to 30 minutes.

1. Turn off the pump. This is not optional. A filter under pressure can launch its lid.
2. Open the air relief valve on top of the filter to release pressure. Wait for the hiss to stop and water to trickle.
3. Open the drain plug at the bottom of the filter tank to let water out.
4. Remove the clamp band or lid ring. Loosen it evenly and lift the top housing off.
5. Lift out the old cartridge or cartridge set. Note how it seats so the new one goes back the same way.
6. Rinse the inside of the tank and check the large O-ring on the lid. Wipe it clean and apply a thin coat of silicone-based pool lube if it looks dry.
7. Drop in the new cartridge, making sure it seats fully on the bottom standpipe and, on multi-element units, that each one clicks onto its manifold.
8. Reassemble the housing, tighten the clamp evenly, and close the drain plug.
9. With the air relief valve still open, turn the pump on. Once a steady stream of water (not air) comes out, close the valve.
10. Note the new clean starting pressure. That number is your future baseline.

Match the replacement to your exact filter. A Hayward Star-Clear Plus C900 Cartridge Filter (90 sq ft) takes a single element, while a Pentair Clean & Clear CC150 Cartridge Filter (150 sq ft) and a large Hayward SwimClear C3030 Cartridge Filter (325 sq ft) use different sizes, and the big multi-element units need the full four-cartridge set. Check the model number on your tank label or the manual before ordering.

Clean or replace: which one do I need right now?

Clean first, almost always. Rinsing between the pleats with a hose removes loose dirt. A soak in a cartridge cleaner dissolves the oils, sunscreen, and scale a hose cannot reach. Skip household degreasers, which can leave residue that foams in the pool.

Reach for a replacement only when cleaning stops restoring pressure, or when the element is physically damaged. Running a dead cartridge wastes energy, because a clogged filter makes the pump work harder for less flow. The Department of Energy notes that filtration and pump efficiency are among the biggest energy costs a pool has, so a freely flowing filter is not just about clear water.

Clear water is also a health basic. The CDC points to proper filtration and testing as the core of safe pool water, so a cartridge that no longer does its job is worth replacing on time. Ready to shop the right size? Browse pool filters and match the square footage to your system. The same clean-first logic works on spas too, covered in hot tub maintenance for beginners.

When in doubt, keep a spare cartridge on the shelf. Swapping in a clean spare while the dirty one soaks means your pool never runs unfiltered, and you always have a backup the day one finally gives out.