Pool & Spa Filter Cartridges

Plan on 1–2 seasons per cartridge in a typical residential pool — the working signal is pressure, not the calendar. Note your filter gauge reading with a clean cartridge, and when it sits 8–10 psi above that baseline and a thorough rinse no longer brings it down, the media is loaded and it is time to replace. Heavy bather loads, pets in the water or a big debris season shorten the clock.

Yes — that is the design. A cartridge has a rinse budget of roughly 4–6 deep-clean cycles: weekly hose rinses lift the loose debris, and a filter-cleaner soak every 4–6 weeks dissolves the oils and scale that water alone cannot. Past that budget the fibers stay loaded, flow stays restricted, and each rinse buys less than the last. Clean it as long as it keeps working; replace it when it stops.

Three measurements: outside diameter of the cartridge, end-cap to end-cap length (not including any protruding pipe), and the square footage printed on the end cap or band label. Note the top and bottom opening types too — open hole, closed with a threaded plug, or a slide-rod handle. Match all three dimensions and the openings; square footage should be equal, never smaller than the original.

They are three numbering systems for the same physical cartridges. Unicel C-#### is the most-cited cross-reference system; Pleatco PA##/PAP### is the OEM-linked line; Filbur FC-#### is the manufacturer-direct system. One cartridge carries all three numbers — type whichever is printed on your old one into the lookup at the top of this page and it lands on the same replacement.

No. A pressure washer concentrates enough force to strip the synthetic fibers and open micro-tears along the pleat edges — damage you cannot see but water can pass through, which means unfiltered water and a gauge that reads clean while the pool turns. A garden hose at 45 degrees with normal household pressure removes everything a rinse can remove. Anything still stuck after that belongs to a chemical soak, not more force.

Not effectively. A torn pleat is an open lane — water takes the path of least resistance and the damaged media stops filtering at exactly the spot it is supposed to work hardest. You will see fine debris returning to the pool and cloudy water that will not clear, while the gauge reads normal. A torn pleat, cracked end cap or collapsed core means the cartridge is done, regardless of age.

The square footage is printed on the end cap or the band label, and it matters more than any other spec. It sets the filter area, which sets how long between cleanings and how hard the pump works. Match it exactly or go up if your housing allows — never down. A smaller-area cartridge loads faster, restricts flow sooner and dies earlier.

Yes — cartridge filtration is standard equipment alongside salt chlorine generators. The routine shifts, not the hardware: salt systems generate chlorine continuously, which loads the media with a steadier chlorine residual, so keep the weekly rinse honest and check the core for corrosion where the metal meets the end caps. Cartridges with reinforced cores hold up better in salt pools.

Usually one of three things: the cartridge was reinstalled with the band or seat misaligned, the o-ring on the tank lid is pinched, or the rinse only cleared the outer pleat faces while the embedded oils remain — the spike is the system telling you the media is still loaded. Re-seat the cartridge, lubricate and re-seat the lid o-ring, and if pressure still climbs within a day, give the cartridge a proper chemical soak.