Spa Filter Cartridge Replacement and Sizing Guide

A filter cartridge is usually replaced when the water stops clearing, not when someone planned to buy one. That timing is why so many replacement enquiries begin with an old part in hand and no reliable number on it. The cartridge that arrives still has to seat in the housing, seal at both ends and carry enough media for the way the spa is used — three separate questions a photograph rarely answers on its own.

Decide whether the cartridge is the part that failed

Sizing only helps if the cartridge is what failed.

Cleaning stops working. If a cartridge responds to cleaning and then falls back quickly, the media is loading faster than it can be cleared.

The media is damaged. Crushed pleats, a split seam, a collapsed core or a torn mesh will not recover.

The ends have degraded. Cracks in an end cap, a worn gasket seat or a deformed thread cause bypass — water travels around the media, and the clarity complaint survives replacement.

The fault is elsewhere. A cracked housing, a damaged standpipe or a split PVC hose keeps water cloudy whatever cartridge goes in. Check the housing and the water pump side of the circuit first.

Size to the housing, not to the label

A part number identifies a family; the housing decides what seats in it. Measure the old cartridge as removed, then check each figure against the proposal.

Length, end cap to end cap. Measure along the media, excluding any handle: a handle adds height above the cap but not to the seated dimension.

Diameter at the widest point. Measure a new or lightly used part; a swollen, loaded cartridge reads larger than the one it replaces.

Top and bottom, separately. For each end record open or closed, hole diameter, any thread, and the gasket or guide that seats it. The ends are often different, and a single “fits either way” note causes wrong supply.

Media area and media weight. Area is quoted in square feet or square metres, weight by the mill in ounces or grams — two identical cartridges can still differ here.

Match the media to the water you are filtering

Three constructions cover most enquiries, and the right one follows what loads the water rather than what sits lowest on a price list.

Pleated cartridges present a folded surface. Debris is held on the outside, which is why they respond to hosing and why a heavy organic load shows quickly as reduced flow.

Mesh-surface cartridges use a smooth surface with a mesh pattern, following the reference supplied. The support structure behind the mesh is part of the specification.

Melt-blown cartridges load through the full wall: microfibre holds particles inside the media rather than on the surface, which suits water where fine turbidity and oils would blind a pleat. The diamond mesh on the outside is the support layer, not an accordion pleat.

Media grade, micron rating and construction are confirmed per enquiry.

Cross-reference the number, then verify the fit

The OEM number on the end cap is the fastest way into a comparison and the least reliable way to finish one: numbers are superseded, and a number read from a faded cap can be a digit out. Use it to establish the family, then confirm length, diameter, both ends and media area. Where a reference has been superseded, ask what changed — it is sometimes the media rather than the fit.

Plan the quantity around how the spa runs

Most housings take a single cartridge; some take a pair, and the pair has to be matched. One in service and one clean and dry keeps a spa running through a cleaning cycle.

On a rental, hotel or swim spa site, the replacement rhythm follows bather load, water chemistry and pre-filtration. Agree one reference and a standing quantity so later orders match the first.

What to send with a replacement enquiry

• The OEM number, and a square-on photograph of the end cap it is printed on.
• Length end cap to end cap and diameter at the widest point, with units.
• Top and bottom ends described separately: open or closed, hole diameter, thread, gasket or guide.
• Media area, media weight or the original specification, if you have it.
• Photographs of the cartridge standing on a flat surface, and of the housing.
• Quantity, destination market and whether the order repeats.

Frequently asked questions

How often should a spa filter cartridge be replaced?

No fixed interval suits every spa. Replace when cleaning no longer restores flow, when the media is crushed, split or torn, or when an end cap, thread or gasket seat has degraded. Bather load and water chemistry move that point considerably.

Can I use a different part number if the dimensions match?

Only after the fit is confirmed. A matching length and diameter does not establish that the ends, the media area or the housing interface are the same. Send the number and the measurements together.

Is a cartridge with more media always the better choice?

Not if the housing cannot take it. Extra length can stop the cap seating and extra diameter can foul the housing wall. The useful question is how much media area fits the housing you have.

Can replacement cartridges be supplied as OEM or ODM?

Yes. OEM and ODM support is available; branding, packaging and order quantity are agreed before production. Standard references can be ordered in small quantities, and OEM runs are agreed per item.

Next step

Review the pleated, mesh-surface and melt-blown options on the filter cartridges page, then send your measurements, end photographs and quantities through contact. If a dimension is unknown, say so — an open question is easier to resolve than a wrong number. For the identification step, see how to identify a spa filter cartridge; for what sits around the filter, the spa components overview is a starting point.

If the complaint is flow rather than clarity, start with how to choose spa jets instead.