Which filter does my Arctic Spas hot tub take? Lookup by year and series

Reviewed October 31, 2026

The right Arctic Spas spa filter depends on the build year and series, not the model name. Spas built in 2008 or earlier use a drop-in, open-ended 50 sq ft cartridge: factory PRT-115LOT, matched by dealers to Unicel C-4950, Pleatco PRB50-IN and Filbur FC-2390. From 2009, and on 2020-and-newer Classic and Core models, the filter screws into the threaded ArcticSpas-logo intake: pleated PRT-900020 or the disposable Silver Sentinel / Atlantis PRT-900007. Open-ended C-4950-type cartridges do not fit that intake. 2020-and-newer Custom Series spas use the Polar Pro system (formerly Pro-Filter).

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The cartridges, with equivalents

Arctic’s owner’s manual does not print filter part numbers, and the Unicel guide has no Arctic table: it points to Blue Falls Mfg. (Canada), Arctic’s maker. The factory numbers and year ranges below come from Arctic Spas dealers; catalog equivalents are from Unicel, Pleatco and Filbur.

Find your year and series

Arctic Spas dealers sort filters by build year and, for 2020 and newer, by series rather than by model name. The one model they single out is the Marmot (see below). Find your era:

How to tell the systems apart

Arctic’s 2026 owner’s manual describes two removal methods. On Custom Series spas you lift out the telescoping insert and the pre-filter, then pull the cartridge up by its handle. On Classic and Core spas you unscrew the cartridge from the threaded intake. Dealers describe the older drop-in filter as an open-ended cartridge that sits in the floating weir well with nothing to screw into. Arctic recommends replacing disposable filters about every three months and rinsing reusable hot tub filters weekly with a deeper clean monthly.

Where the sources disagree

• Where the drop-in years start and end. Arctic Spas Ontario says “2008 or earlier”; arcticspastore.com and Premier say 1998 through 2008. Arctic Spas Spokane’s parts site lists the drop-in weir parts for 2002–2008 and the threaded weir assembly for 2011–2019, which leaves 2009–2010 unclear there. Every source agrees the threaded intake was in use by 2011.
• The Marmot. Two dealers exclude the Marmot from the 1998–2008 drop-in Silver Sentinel, and none of the sources we found says what the Marmot takes.
• 4CH-949 for Arctic. Premier names Unicel 4CH-949 for 2009–2019 and Classic/Core spas. Arctic Spas Ontario sells only the factory PRT-900020 for the threaded intake, and the Unicel guide lists 4CH-949 for Waterway, Dynasty and Rising Dragon, not Arctic or Blue Falls.
• C-4310. Unicel’s Blue Falls list includes a small C-4310 (4-1/4" × 4", 10 sq ft); Premier states “C-4310 is not the correct filter” for these Arctic spas.
• 25 or 50 sq ft drop-in. Unicel and Filbur list both C-4326 (25 sq ft) and C-4950 (50 sq ft) for Arctic. They are the same size; the dealer factory filter is the 50 sq ft PRT-115LOT.
• Pro-Filter vs Polar Pro. arcticspastore.com says the original Custom Series Pro-Filter set is discontinued in favor of Polar Pro and that its older pre-filter is not compatible with Polar Pro. Arctic Spas Ontario still sells Pro-Filter 2-packs for all 2020+ Custom Series spas. Match the insert to the housing you have.

Known limits

• Arctic Spas does not publish a part-number chart; the factory numbers here come from dealers, and the manual gives no part numbers.
• No source gives filter area for the Silver Sentinel, Atlantis or Polar Pro filters.
• Only the drop-in C-4950 and C-4326 cartridges are in our dataset for Arctic; the threaded and Polar Pro filters have no catalog cross-reference.

How to confirm yours

1. Look at the intake: an ArcticSpas logo with threads means the threaded filter; an open well with no thread means the drop-in; a telescoping insert and pre-filter means Custom Series Pro-Filter or Polar Pro.
2. Read the number on the old filter and search it here, or measure it with our filter-size guide. Our open-end vs threaded guide explains why an open cartridge will not seal on a threaded intake.
3. Compare with the Arctic Spas brand table.

Why one cartridge size can carry two different square-foot ratings: our explainer with Unicel’s pleat-count table.

Sources

1. Arctic Spas: Owner’s manual, international edition V0504-2026 (filter removal by series, care intervals)
2. Arctic Spas Ontario: Filter 50 pleated drop-in (PRT-115LOT; C-4950 / PRB50-IN / FC-2390; 2008 or earlier)
3. Arctic Spas Ontario: Filter 50 pleated thread-in (PRT-900020; open-core cartridges do not fit)
4. Arctic Spas Ontario: Silver Sentinel thread-in (PRT-900007, replaces PRT-900003; no aftermarket equivalent)
5. Arctic Spas Ontario: Polar Pro filters (2020+ Custom Series)
6. Premier Pools & Spas: Arctic Spa filters 2009–2019 and 2020 Classic and Core filter guide (4CH-949, C-4310 note, Rescue Bag filters)
7. Premier Pools & Spas: New Arctic Spas Polar Pro filters for Custom Series spas (PRT-900150, -900140, -900170, -900180, -900190)
8. Premier Pools & Spas: Arctic Silver Sentinel drop-in PRT-900004 (1998–2008, not Marmot)
9. Premier Pools & Spas: Arctic Atlantis drop-in PRT-900008 (1998–2008, not Marmot)
10. Arctic Spas Spokane: Arctic parts: filters and weir parts by year
11. Unicel 2026 Replacement Guide: Arctic Spas entry pointing to Blue Falls Mfg. (printed pp. 24–25) and spec tables
12. Filbur Catalog & Reference Guide: Arctic Spas and Blue Falls Mfg. (printed p. 27)

This page summarizes published catalogs and dealer fitment tables; always follow your own spa’s owner’s manual. See our disclaimer and methodology.