The Best Master Spa Filter Replacements

The verdict, up front. There is no single “Master Spa filter.” The brand has used at least three physically different cartridge shapes across its ranges, and two of its systems take two filters rather than one. Almost every wrong order in this category comes from buying by tub brand instead of by part number.

So the honest version of this page is a matching exercise first and a shopping list second. Read the number printed on the cartridge you are taking out, measure its length and the holes at each end, and then pick the listing below whose stated numbers match yours. If the old filter is long gone, the measuring section below gets you there with a tape.

How we judged these

Work out which shape your tub takes

This is the whole job. Master Spa cartridges divide into three families and they are not interchangeable in any direction:

• Open-ended drop-in. A cartridge with an open hole at both ends that drops into the housing. The current Eco-Pur shape is this type, roughly 6 3/4 inches long and 8 inches across with 4 1/16 inch openings.
• Threaded with a handle. Used on the Legacy and Freedom ranges. It screws into a 2 inch threaded fitting at the base and has a carry handle molded into the top. Physically nothing like the drop-in type.
• Small inner element. Around 7 inches long and only 3 7/8 inches across, in the PMA10 pattern. On the tubs that use one, it sits alongside a larger outer filter rather than replacing it.

If you still have the old cartridge, this takes ten seconds: a handle and a screw thread means the Legacy and Freedom part, an 8 inch diameter with open ends means the current Eco-Pur shape, and anything under 4 inches across is the small inner element. If you do not, lift the filter lid and measure the housing before ordering anything.

The two-filter trap

Eco-Pur systems introduced from 2007 onward often run an outer cartridge and a separate inner element together. This catches people out for an obvious reason: they buy one filter, fit it, and the tub still never quite clears, because half the filtration in the housing is several years old and blinded off.

Before you order, take the whole assembly out and count what is in it. If there are two elements, both need replacing on the same schedule. This is also the most common reason a Master Spa owner concludes that aftermarket filters “do not work” — the new one is fine, and the one they did not replace is the problem.

OEM part numbers, and why they multiply

Master Spa parts carry X-numbers: X268330, X238330, X268325, X268370, X268380 and others, and several of them refer to the same physical cartridge sold at different times or in different packs. The aftermarket then adds its own naming on top — Pleatco PMA-something, Unicel C-something, Filbur FC-something — so one filter can legitimately carry six numbers.

That is why cross-reference clarity is our first criterion rather than build quality. A well-made cartridge in the wrong shape is worthless, and the only defense against the wrong shape is a listing that prints the whole chain of equivalents so you can find your number in it. Every pick below does, which is a large part of why they are the picks.

OEM or aftermarket?

The cartridges on this page are aftermarket, which is why they cost meaningfully less than the dealer parts. That is a reasonable trade for most owners: a filter is a consumable, and a cheaper one that actually gets changed on schedule beats an expensive one stretched to eighteen months.

There are two honest caveats. Aftermarket end caps are generally the first thing to go, so inspect the cap-to-media bond each time you clean one. And an independent test standard is rare here — only one pick below cites testing to NSF 50 protocols, which is worth something in a category where almost everything else is sold on adjectives.

Filtration is not sanitation

Worth stating plainly, because filter pages attract the belief that a better cartridge means less chemistry. A filter removes particles. It does not disinfect, and public health guidance for hot tubs is built around holding a measurable sanitizer residual at a controlled pH.^[source] The targets are pH 7.2 to 7.8 with at least 3 ppm free chlorine, or 4 to 8 ppm bromine, whatever cartridge is fitted.^[source]

What a clean, correctly fitted filter does is let the sanitizer work on dissolved load instead of suspended dirt. That is real, and it is a different claim.

How often to change them

Clean on a schedule, replace on condition. A rinse every couple of weeks and a proper chemical soak every few months keeps a cartridge working; our guide to cleaning a filter covers the soak, and filter cleaners covers what to soak it in.

Replace when the pleats stay grey after a soak, when the media feels stiff, or when the end cap has started to separate. On a tub that takes two elements, replace both at once. The full picture is in when to replace a hot tub filter, and if you run a two-filter rotation, the cadence changes again — which is one argument for buying the multi-packs on this page.

On prices, and on what these scores are

Master Spa replacements run from inexpensive for a small inner element to mid-range for a current Eco-Pur cartridge, and the multi-packs are where the per-filter cost improves. Every button reads the live price where our price layer has one; anything we cannot verify, we do not print — the reasoning is on how we pick.

The scores are an editorial judgment of published cross-references, stated dimensions, construction detail and pack economics, against our published method. We have not tested these cartridges, we make no performance claims on their behalf, and there is no rating markup in this page’s structured data.

The honest summary

For most current Master Spas, the drop-in Eco-Pur cartridge is the part, and its listing prints enough cross-references to check before you buy. If your filter screws in and has a handle, you have a Legacy or Freedom and you need the threaded one instead. If the housing contains two elements, buy both. And if you are not sure which of those you have, the tape measure answers it faster than any part number search will.

The general version of this problem — matching any cartridge to any tub — is what our hot tub filter finder is for.