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31CARTRIDGE spa filter equivalents
Part number 31CARTRIDGE appears in 1 cross-reference row below. Each row lists the OEM, Unicel and Pleatco numbers that the source documents treat as interchangeable, plus the cartridge size so you can confirm against your old filter.
The same numbers, on one page, are in the cross-reference lookup. A schedule for this part number, and the buy link, are on the replacement schedule and reorder page. Published intervals by brand are in the replace and clean calculator.
Nordic Hot Tubs C-4326 cartridge, 4-15/16" (125 mm) × 13-5/16" (338 mm), 25 sq ft. Unicel C-4326, Pleatco PRB25-IN.
Unicel C-4326
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| OEM | 31CARTRIDGE |
|---|---|
| Unicel | C-4326 |
| Pleatco | PRB25-IN |
| Filbur | FC-2375 |
| Size | 4-15/16" (125 mm) × 13-5/16" (338 mm), 25 sq ft |
Sources
- Unicel 2026 Replacement Guide: OEM cross reference (Nordic Hot Tubs section), PDF p.46 (printed p.42); spec table PDF p.9 (printed p.5) (PDF)
- Pleatco 2023 Catalog: Unicel-to-Pleatco cross reference, PDF p.47 (C-4326 = PRB25-IN) (PDF)
- Filbur Catalog & Reference Guide: Product by Pool/Spa Manufacturer (OEM), Nordic Hot Tubs, printed p.44 (PDF p.23) (PDF)
- Nordic Hot Tubs filter chart (2023): CARTRIDGE row: Unicel C-4326, Pleatco PRB25-IN, Filbur FC-2375, Waterway 817-2500; model list, before/after Sept 2021 notes (PDF)
- Nordic Hot Tubs 2022 service parts list: 31CARTRIDGE, Cartridge, Filter, 25 SQ FT (PDF)
Not in sources: Nordic's chart does not use the catalogs' 7/99 date and gives no years for most models; Nordic's owner's manual lists Impulse under CARTRIDGE-E while the chart lists it here.
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