Clean it or replace it
Hayward’s SwimClear manual puts the two choices in one sentence: when the gauge reads 7 to 10 psi above the starting pressure, or flow drops below the rate you want, “clean or replace the filter cartridge.” The gauge tells you something is due. It does not tell you which. That depends on what happens after a proper clean, which means a degreaser soak and not just a hose-down. The cleaning guide has the method.
None of the makers we checked prints a lifespan in years. Hayward’s own sell sheet promises “multi-season durability” and stops there. Unicel, which makes replacement cartridges, gives three triggers instead: the time between cleanings keeps getting shorter, flow is low and pressure is high, or the cartridge fails outright with a torn fabric or a collapsed centre core.
| What you see | What it means | Action |
|---|---|---|
| Pressure drops back after a proper clean | Dirty, not finished | Clean on schedule and refit |
| Cleaned, but runs between cleanings keep shrinking | Media worn out | Replace |
| Low flow and high pressure straight after a clean | Media worn out or blinded | Replace |
| Tear in the fabric, or a collapsed centre core | Failed outright | Replace now |
| Pleat bands loose or missing | Often a sign of wear | Inspect closely, plan a replacement |
| One band split, everything else sound | Unicel says this does not affect filtration | Keep using it |
The comparison that settles it is the clean reading written on the housing. If a cleaned cartridge cannot get back near that number, it is finished. The pressure gauge guide covers that baseline, and why a low reading points somewhere else entirely.
Start with the part number
Before you reach for a tape measure, look at the end cap. Hayward moulds its product information into the caps, and Unicel and Pleatco both mark a part number on theirs. If the old part number is legible, a cross-reference does the rest. Pentair’s Pleatco finder searches by part number, by filter manufacturer, or by diameter and length.
The filter’s own model number works too, and it explains square footage better than any rule. Hayward’s SwimClear C4030 is rated at 425 square feet. Hayward’s cartridge sheet says it takes four CX880XRE elements, and Unicel lists that element at 106 square feet each: 7 in. across and 25-1/2 in. long. Four of them add up to the housing’s 425, give or take rounding. The number on the filter is the total of its elements, so a replacement with less area per element means less filter.
Measuring when the label is gone
Unicel’s replacement guide gives five measurements, in this order:
- Outside diameter, to within 1/32 in.
- Length, to within 1/16 in., including the end caps but not the handles or any other extension. Measure through the centre if you can, not along the outside edge.
- End cap style, top and bottom. Where an end is open, measure the inside diameter of the opening to within 1/32 in.
- The make and model of the filter it came out of, if you can find them.
- Pleat count (to within two), and whether it has a centre core.
Do it with the old cartridge in your hand
Measure it before it goes in the bin and write the numbers inside the equipment-pad lid or in the client’s file. On a route, the next replacement is then a two-minute order instead of a second visit.
OEM vs aftermarket, honestly
Both sides make claims. Hayward says its genuine cartridges are “the only replacement cartridges that maintain the original filter fit and performance”. Unicel says its end caps follow “exact OEM design and material specifications.” Those are sales claims, and neither of them answers the question that matters on the pad: does this cartridge have the same dimensions as the one you took out?
Unicel’s own guide is the best argument for checking. For Hayward’s SwimClear C150S it lists two options. One matches the original 10-5/16 in. diameter. The other, listed as an “alternative”, is 8-15/16 in. across, and a note says its core support “must be knocked out before installation.” Both are listed honestly, but only one is a like-for-like swap. Unicel’s guide also lists a fabric weight in ounces for every cartridge, so compare that as well as the size.
The practical rule: an aftermarket cartridge that matches the diameter, length, end caps, area and media weight is a fair swap. One that is only an “alternative” is a compromise you should choose on purpose. Fit is where the money is lost. A cartridge that does not seal at the end caps lets water go around the fabric, and the gauge will not show it. Cloudy water will, eventually. If the water turns dull after a new cartridge goes in, check the seating first, then work through cloudy pool water.
Rotating two sets
Hayward calls a spare element “an excellent investment”, and Unicel’s advice is to “alternate two sets of cartridges when cleaning.” The reason is in Hayward’s own cleaning note: a cartridge is easier to clean when it is dry. With two sets, the dirty one comes off, the clean one goes straight in, and the dirty one gets its soak and dries properly instead of going back in damp the same afternoon.
Mark the sets A and B on the end caps and log which one is in the filter. Then the “runs keep getting shorter” sign from the table above becomes something you can actually see in your notes. When you refit, clean out any debris from the bottom of the housing and seat the cartridge evenly on its hub. Check that the head (lid) O-ring is clean and in place, and write down the reading with the new cartridge as your next clean baseline. If you are weighing a switch away from cartridges altogether, the filter comparison sets out the trade, and the turnover calculator checks whether the housing is being over-driven.