How to Replace a Pool Filter Cartridge

How do you replace a pool filter cartridge?

Start by shutting off the pump and opening the air relief valve on top of the filter to bleed off pressure. Never open a filter that is still under pressure; the lid or clamp can let go with real force. Once the hissing stops and the gauge reads zero, pull the drain plug at the bottom of the tank and let the water drain down below the lid seam so it does not pour out when you open it.

Next, release the clamp band or lid lock and lift the top half of the tank off. Most cartridge filters use a stainless band clamp with a single bolt, or a large threaded lock ring you turn by hand. Set the lid aside without dragging it across the sealing surface. With the lid off you can grip the old cartridge and pull it straight up and out; on a multi-cartridge filter you lift the top manifold off first, then pull each element. Hose the empty tank out and wipe the sealing groove clean.

Before the new cartridge goes in, inspect and lube the main tank O-ring with a silicone lubricant, never a petroleum product (petroleum swells and ruins the rubber). Check the standpipe O-ring at the base too, since a nick there lets unfiltered water bypass the cartridge. Seat the new cartridge squarely over the standpipe, set the manifold and lid back on, draw the clamp down evenly, then close the drain, open the air bleed, and restart the pump. Let it push the air out until a steady stream of water comes from the bleed valve, close it, and note the new clean baseline pressure on the gauge.

When should you replace a cartridge instead of cleaning it?

Replace the cartridge when a proper cleaning no longer restores flow, not on a fixed date. A cartridge you can hose off and soak is still good; one that climbs back to high pressure within days of a deep clean is worn out. The quickest test is the one you already do for service: if the gauge sits 8 to 10 PSI above its clean baseline again almost immediately after cleaning, the fabric is clogged at a level a soak cannot reach. Work through the high filter pressure guide first to rule out a closed valve or other cause.

Clean before you condemn it. A hose rinse removes dirt but not the body oils, sunscreen, and scale that actually clog the pleats, so a cartridge that seems dead often comes back after an overnight soak in filter cleaner. The full method, and which cleaner to use, is in the filter cleaning guide. Only after a real deep clean fails to drop the pressure is the cartridge genuinely done.

Look at the cartridge itself, too. Matted or splayed pleats that no longer stand up, tears or thin worn spots in the fabric, cracked end caps, or a broken band all mean replace it, because a damaged cartridge lets dirt straight through no matter how clean it is. Pleated cartridges are consumables with a service life measured in years, so plan on replacement as part of owning the pool, not as a failure.

How do you know which replacement cartridge to buy?

Cartridges are not interchangeable, so match the replacement one of two ways. The reliable way is the part number: read the number printed on the end cap of the old cartridge, or find your filter's model number on the tank label, then cross-reference it. The aftermarket is built around three cross-reference brands, Unicel (numbers like C-7470), Pleatco (PLF or similar), and Filbur (FC series), and every listing shows which OEM cartridge and which of the other brands it replaces. Match any one of those numbers and the fit is guaranteed.

If the number has worn off, measure four things: the outside diameter, the overall length from end cap to end cap, the top end-cap style (an open hole, with or without a molded handle), and the bottom end-cap style (open, or closed with a small hole for the standpipe). Those four measurements plus the thread or tube size pin down the exact cartridge. A quarter inch off on length and the lid will not clamp down; the wrong end cap and it will not seal to the manifold.

The one spec worth upgrading rather than just matching is square footage, which must meet or exceed the original. More filter area means longer runs between cleanings and finer filtration, so never drop to a smaller cartridge to save a few dollars. If the whole filter feels undersized for how often you are cleaning it, that is a sign to size up the unit itself rather than the cartridge; the pool filter guide covers how to size a cartridge filter, and the sand versus cartridge comparison is worth a look if you are rethinking the filter type entirely.

Do you replace all the cartridges at once?

On a multi-cartridge filter, yes, replace all of them as a set. Large filters like the Pentair Clean and Clear Plus, Hayward SwimClear, and Jandy CV series hold four cartridges stacked between a top and bottom manifold. They all did the same work over the same years, so if one is worn the others are close behind, and mixing a new cartridge with three tired ones throws off the even flow the stack depends on. Buy the set, not a single element.

A single-cartridge filter, such as a Hayward Star-Clear Plus or a single-element Pentair Clean and Clear, is simpler: one cartridge comes out and one goes in. Either way, this is the moment to check the standpipe and manifold O-rings and the air relief assembly while the tank is open, since a cheap O-ring is far easier to swap now than after you have buttoned everything up and found a leak.

When you reassemble a four-cartridge filter, make sure each element seats fully onto the bottom manifold before you lower the top manifold, and that the top manifold sits flat before the lid goes on. A cartridge that is cocked or not fully down holds the lid off its seal and leaks, which is the most common reason a fresh set seems to fail on the first restart.

How much does it cost to replace a pool filter cartridge?

A single standard cartridge runs about $20 to $80, a large single element runs roughly $60 to $150, and a full set of four big cartridges for a large filter runs about $150 to $400. The spread is driven by square footage and brand: a small above-ground cartridge is cheap, while a set for a 400-plus square foot in-ground filter is the top of the range. Since the swap takes about 20 minutes with no special tools, the cartridge itself is essentially the whole cost.

You can usually save money with a quality aftermarket cartridge instead of the OEM part, as long as the cross-reference number and the square footage both match. The caution with the cheapest generics is thinner fabric and less actual media than the label claims, so they clog sooner and need replacing more often; a mid-priced Unicel, Pleatco, or Filbur equivalent is the sensible middle ground. A good cartridge that is cleaned on schedule lasts years, so paying slightly more for one that holds up is usually the cheaper path over time.

There is no real reason to hire this out, because the swap is one of the easiest jobs on the equipment pad once you have the right cartridge in hand. The money and the mistakes are all on the purchase side: buy the matching size and end-cap style the first time, keep it cleaned so it reaches its full life, and the replacement is a 20-minute afternoon job.

Frequently asked questions