Pool Filter Cartridge (2026): Match Size Before You Replace It

Cartridge filters only work when the element fills the tank the way the designer intended. A cartridge that is a half-inch short bypasses dirty water. One that is too fat will not seat. Start with the model sticker on the tank or the pump, then measure the old element: length, outer diameter, and the inside diameter of each end cap. Square footage is the last check, not the first.

If you are still on the tiny pump that came with an Easy Set, you are shopping a different product than an in-ground Clean & Clear. Sand filters are a third path entirely, covered in our best pool filter guide. These picks come from live US Amazon listings, published dimensions, and owner-review patterns. We did not pressure-test the tanks.

Measure twice, then match the family

Pull the dirty cartridge after you shut the pump off and release pressure. Do not force a clamp on a pressurized lid. Lay the element on a tape measure.

Write down:

• Length
• Outer diameter
• Top hole and bottom hole (open, closed, or a threaded pin)
• Any OEM number on the end cap

Then match a known family. Guessing “75 square feet” from a forum post is how people order a Hayward pack for a Pentair tank.

Three common backyard sizes

Intex Type A or C Filter Cartridge 6-Pack is the above-ground answer. These are the short 8 by 4.25-inch elements for 530 to 1,500 GPH Intex cartridge pumps. They are not reusable the way a $70 in-ground cartridge is. You rinse them, then you replace them. A six-pack exists because a busy week of sunscreen and grass clippings loads them fast. If your pump says Type B, do not buy this pack.

Unicel C-9407 is the 75 square foot cartridge for Pentair Clean & Clear 75 and Predator 75 tanks. Dimensions are about 16-1/8 inches long and 10-1/16 inches across, with 6-inch open ends. Cross-references include PAP75 and Filbur FC-0685. Buy it when those numbers match your old element. Skip it for a 100 or 200 square foot Clean & Clear Plus. Those tanks use a different Unicel number.

Hayward CX580XREPAK4 is four elements for SwimClear C3020, C3025, and C3030 tanks. Each cartridge is about 19-5/8 by 7 inches. The pack is expensive because the filter needs all four. Ordering one Unicel “because it was cheaper per square foot” leaves three bays empty. Confirm the Hayward model before you click.

Replace when cleaning stops working

Rinse pleats with a garden hose from the inside out when the pressure gauge is about 8 to 10 psi above the clean baseline. Soak with a cartridge cleaner if the media is greasy. When the band breaks, the core folds, or the clean pressure never returns, replace the set.

Keep a spare for in-ground tanks so you can swap and soak the dirty set overnight. For Intex Type A, keep the six-pack closed until you need the next one. Sun-rotted plastic end caps crack.

A new cartridge will not fix a dead impeller or a sand filter that needs new media. It also will not balance pH. Put chemistry on a test kit and put the right element in the right tank.

Seat it so water cannot sneak around the pleats

Drop the cartridge straight onto the standpipe or into the pump basket housing the way the manual shows. A tilted element leaves a gap. On Intex-style pumps, seat the Type A/C cartridge so the handle or open core lines up with the lid. On a Clean & Clear, the large open ends must sit on the manifold, not on a wad of old o-ring grease.

Lubricate tank o-rings with a pool-safe lubricant if the manufacturer calls for it. A dry, pinched ring leaks even with a brand-new Unicel inside. That leak looks like a “bad cartridge” in the first hour.

Write the install date on the end cap with a marker. When pressure climbs fast again, you will know whether you got three months or three weeks. Heavy bather load, storms, and algae blooms shorten life. A phosphate treatment or a clarifier dose can also load pleats quickly. That is expected. Rinse sooner rather than running a bypass around packed media.

Keep the box for the part number. Next season you should not have to guess among C-9407, C-9410, and a Hayward four-pack because the Amazon photo looked similar. If you ever switch from cartridge to sand, you need different equipment, not a different pleat. A robot cleaner still belongs on the weekly schedule. Fine dust that the cartridge misses is often leftover after a storm, not a reason to buy a random “universal” element.

Bottom line

Order a pool filter cartridge by dimensions and model, not by a generic square-foot search. Intex Type A/C six-packs cover small above-ground pumps. Unicel C-9407 covers the Pentair 75 size. Hayward CX580XREPAK4 covers SwimClear four-packs. Measure the old element, then buy that one.