The Best Softub Filter Replacements

The verdict, up front. Softub filter buying comes down to one question: was your tub built before or after July 2009?

• July 2009 and later — part 5020, also carrying the number 8553, listed at 35 square feet and covering the T-140, T-220 and T-300 models.
• Before July 2009 — part 5015, a different cartridge that the newer one will not substitute for.

Search for “Softub filter” and nearly everything returned is the 5020, because that is the larger market. Owners of older tubs order what comes up first, find it does not fit, and conclude the listing was wrong. It was not — it was for the other half of the fleet.

How we judged these

Finding out which side of 2009 you are on

The reliable answer is the number on the cartridge you are removing. If it is gone or illegible, work from the tub instead: Softub’s model designations on the current filter listings are T-140, T-220 and T-300, so a tub badged with one of those is on the later part.

If your Softub predates that naming, or you bought it second-hand with no paperwork, buy one 5015 and one 5020 rather than guessing twice. These are inexpensive cartridges and the shipping on a wrong-part return will cost more than the spare.

Why a Softub filter is different

Softub is a soft-sided tub with its pump, heater and filter in a separate motor pack rather than in a cabinet around the shell. That has two practical consequences for filtration.

First, the cartridge is small. At 35 square feet it is around half the media of a mid-size hard-shell spa filter and a fraction of the 75 square foot elements used by brands like Sundance. Less media means it loads up faster, so the cleaning and replacement interval is genuinely shorter — this is not a filter you inspect twice a year.

Second, the motor pack is where the heat is. A blinded filter restricts flow, and restricted flow through a compact heater arrangement is worth avoiding for reasons beyond water clarity. If your Softub is cutting out or struggling to hold temperature, the filter is the first thing to check, not the last.

Small filter, faster rhythm

• Rinse weekly rather than fortnightly. A 35 square foot cartridge does not have the reserve that a big one does.
• Soak chemically every few weeks, not every few months. The method is in how to clean a hot tub filter and the products in the best filter cleaners.
• Own two. A two-filter rotation matters more on small cartridges than large ones, because you are taking the filter out more often and a damp filter refitted immediately never fully recovers.
• Replace on condition. Pleats that stay grey after a soak, stiff media, or a separating end cap — the signals are in when to replace a hot tub filter.

On the antibacterial claim

Softub cartridges are sometimes described as antibacterial, though no listing on this page currently carries the description. Treat it as a manufacturer claim rather than a verified property wherever you meet it: we have not seen a test behind it and we are not going to imply one exists.

More importantly, an antibacterial treatment on filter media is not a sanitizer and changes nothing about what you hold in the water. Hot tub guidance is built on a measurable residual at a controlled pH — pH 7.2 to 7.8 with at least 3 ppm free chlorine, or 4 to 8 ppm bromine.^[source] A Softub’s small water volume actually makes that discipline more important, not less, because a smaller body of water swings faster with bather load.

OEM or aftermarket?

Everything on this page except the Darlly cartridge is aftermarket, and for a consumable at this price that is a reasonable default. The best of these listings are more informative than the generic ones, stating the month of the cutoff, the T-series models and the filtration area.

Darlly is a long-established cartridge manufacturer rather than a relabeler, which is worth something if you would rather buy a known filter brand. The honest counterweight is that we have no published evidence it filters differently, and it costs more than the generic equivalents.

On prices, and on what these scores are

Softub cartridges are inexpensive individually and add up because you change them often. The older 5015 costs more and is stocked less reliably, which is a market effect rather than a quality one. 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 fit information, stated cross-references, construction and pack economics, against our published method. We have not tested these filters, we make no performance claims on their behalf, and there is no rating markup in this page’s structured data.

The honest summary

Establish the date first. From July 2009 onward you want the 5020, and the listings that name the T-140, T-220 and T-300 models give you the most confidence you are looking at the right one. Before that, you want the 5015, and it is worth buying a spare while you can see one in stock.

Then adjust your expectations on interval. A 35 square foot cartridge in a hard-working motor pack is a faster consumable than a hard-shell spa’s filter, and owning two is the cheapest way to make that manageable.