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Thermo Spas Filters

ThermoSpas hot tubs (Park Avenue, Concord, Manhattan, Gemini, Healing Spa, Olympian and the Aquacisor swim spa) take small cartridges: a screw-in with a 2″ thread (5″ or 6″ across, closed top or handle) or an open drop-in that lifts out (one long cartridge, or two short ones stacked). Look at the bottom and the top of your old filter.

Find your ThermoSpas filter in 10 seconds

All six ThermoSpas cartridges are offered in ProAqua (high-flow); the closed-top 25 is also in Darlly. Drop-shipped from US stock. If yours matches none of the cards, send a photo through the form below.

Shop: All Hot Tub Filters | Ego3 Reusable Filters

Resources: Compare Filter Brands | Water Care

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✅ Not Sure It Fits? Verify Before Ordering

Hot tub filter fitment varies by spa brand, model, year, filter size, thread style and top/bottom style.

To confirm the correct replacement, send clear photos of:

  • The label or end cap of your current filter
  • Your spa serial number sticker
  • The filter well with the filter removed (so we can see the fitting)

EZ Hot Tub Parts confirms fitment before you order, so you do not pay return freight on a wrong filter.

Thermo Spas filter buying guide

Screw-in, 2″ thread. Three cartridges: 4-15/16″ × 6-5/8″ 25 sq ft with a closed top and no handle (Unicel 4CH-23, Pleatco PFF25TC-P4, Filbur FC-2400) — ProAqua / Darlly; 6″ × 7-1/8″ 25 sq ft with a handle (Unicel 6CH-26, Pleatco PTL25W-SV) — ProAqua; and 6″ × 9-7/8″ 35 sq ft (Unicel 6CH-35, Pleatco PTL35W-P-4) — ProAqua. Diameter and top style decide it.

Drop-in, 4-15/16″ across, open both ends. One long 14-7/8″ cartridge at 28 sq ft (Unicel C-4301, Pleatco PMT27) — ProAqua; or stacked short pairs: 6-5/8″ tall 50 sq ft (Unicel C-4405, Pleatco PRB25SF-PAIR) — ProAqua, 4-5/8″ tall 35 sq ft (Unicel C-4401, Pleatco PRB17.5SF-PAIR) — ProAqua. If two cartridges came out of one well, replace both.

Not sure which filter brand is right for you? Compare Hurricane, OEM Factory Direct, Pleatco, ProAqua, Darlly and Ego3.

Keep your filters working longer: High Pressure Filter Nozzle | Filter Cleaner | Water Care — and every order over $99 ships free, so a spare set plus cleaner usually rides along at no extra cost.

Confirm your ThermoSpas filter: 25 Closed Top | 25 Handle | 35 Thread | Drop-In 28 Long | Drop-In 50 Pair | Drop-In 35 Pair

Thermo Spas filter questions

How do I identify my ThermoSpas filter?

ThermoSpas did not tie one cartridge to one model name, so identify by the filter itself. Bottom first: a 2″ threaded nipple means screw-in; open holes at both ends mean drop-in. Then the top: closed solid cap (25 sq ft, 5″ across) or a handle (6″ across). For drop-ins, one long 14-7/8″ cartridge is the 28 sq ft; two short ones stacked are the 50 or 35 sq ft pairs. Send a photo through the form above if unsure.

What are the Thermo Spas filter part numbers?

25 closed top: Unicel 4CH-23, Pleatco PFF25TC-P4, Filbur FC-2400. 25 handle: Unicel 6CH-26, Pleatco PTL25W-SV. 35 thread: Unicel 6CH-35, Pleatco PTL35W-P-4. Drop-in 28: Unicel C-4301, Pleatco PMT27. Pairs: Unicel C-4405 / Pleatco PRB25SF-PAIR and Unicel C-4401 / Pleatco PRB17.5SF-PAIR.

Do I have to replace both ThermoSpas drop-in filters at once?

Yes when two short cartridges share one well — a new one on top of a clogged one just forces all the flow through the new one. The 2 packs are priced for exactly that.

How often do ThermoSpas filters need changing?

Rinse every 2–4 weeks, soak monthly in filter cleaner, replace every 12 months or when the pleats stay grey. Small cartridges load up faster than big ones, so keep a spare set.

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