Discontinued spa filter numbers: what Unicel and Pleatco list as the replacement
When a spa filter number is discontinued, the maker usually names one replacement, and it is not always the same size. Unicel’s 2026 guide prints a “discontinued … use” note under each retired cartridge and a matching “USE” line in its price index[5]; Pleatco’s 2023 catalog has a “Deactivated Pleatco part numbers” table[2]. Several of Unicel’s skim-filter replacements are threaded MPT cartridges that need the old PAD adapter removed from the skim well, and some replacements have a different filter area (C-5302 at 50 sq ft becomes C-5624 at 25). Check the table below, then compare the new part’s size and bottom fitting against your old cartridge before you order.
A cartridge number that no longer turns up anywhere is usually not a dead end. Unicel and Pleatco both publish what they want you to buy instead. This page collects the spa and hot tub filter numbers from those lists, with the old and new specs side by side, so you can see what changes. The sources are the Unicel 2026 Replacement Guide (spec-table notes and price index)[5], the Pleatco 2023 catalog[2] and, for the adapter step, the Filbur catalog[31].
Unicel: discontinued spa cartridges and the named replacement
| Discontinued | Old cartridge (Unicel spec row) | Unicel says use | What changes |
|---|---|---|---|
| C-4303 | 4-5/8" × 6-3/4", molded cone handle, 15 sq ft. Pleatco skim filter, Softsider, Vita | 4CH-20 if the PAD adapter is MPT | Threaded 1-1/2" MPT, 20 sq ft. Remove the threaded PAD adapter from the skim well. |
| C-4324 | 4-5/8" × 9-3/4", molded cone handle, 25 sq ft. Skim filter, Spa Manufacturers, Gatsby | 4CH-24 if the PAD adapter is MPT | Threaded 1-1/2" MPT, same 25 sq ft. Remove the PAD adapter. |
| C-4431 | 4-15/16" × 10-3/8", closed top, 30 sq ft. Skim filter, Lifestyle | No replacement named | Match by size (how to measure) |
| C-4430 | 4-15/16" × 11-7/8", 2-1/8" open, 30 sq ft. Santanna | C-4332 | Same size, 32 sq ft |
| C-4347 | 4-15/16" × 14-7/8", 2-1/8" open, 45 sq ft. Santanna | C-4305 | Same size, 50 sq ft |
| C-4970 | 4-15/16" × 23-5/8", 2-1/8" open, 75 sq ft. Waterway | C-4995 | Same size, 95 sq ft |
| C-5615 | 5" × 13-5/16", 2-3/8" open, no center core, 15 sq ft. Jacuzzi CFR-15 in-line | Spec note: C-5625 (25 sq ft). Price index: C-5635 (37 sq ft) | The two Unicel lists disagree. Both are the same 5" × 13-5/16" size. Jacuzzi also discontinued the CFR-15. |
| C-5636 | 5-3/16" × 19-5/8", 1-1/16" open, 6 oz media, 36 sq ft. Marquis | C-5637 | Same size, 4 oz media, 40 sq ft |
| C-5302 | 5-3/4" × 11-7/8", 2-1/8" open, 50 sq ft. Teledyne Spa Pak | C-5624 | Same size, but 25 sq ft |
| C-6601 | 6" × 9-3/4", 4 oz, 25 sq ft. Four Seasons, Aqua Spa | Spec note: 6CH-35 (35 sq ft) or 6CH-47 (47 sq ft) if the PAD adapter is MPT; 6CH-940 if it is SAE. Price index omits 6CH-47. | Threaded replacements; check the thread on your adapter |
| C-6450 | 6" × 13-7/16", molded cone handle, 50 sq ft. Pleatco skim filter, Hercules | 6CH-50 if the PAD adapter is MPT | Threaded, 50 sq ft. Remove the PAD adapter. |
| C-6475 | 6" × 14-3/4", 75 sq ft. Advanced Spa | 6CH-50 if the PAD adapter is MPT | 6" × 13-7/16", 50 sq ft, shorter. Remove the PAD adapter. |
| C-7432 | 7" × 8", 4 oz, 32 sq ft. Softsider, Pleatco skim filter | 7CH-32 (1-1/2" MPT) or 7CH-322 (2" MPT) | Pick by the thread on your PAD adapter, then remove it |
| C-7439 | 7" × 9-3/4", 4 oz, 40 sq ft. Softsider, Pleatco skim filter | 7CH-40 (1-1/2" MPT) or 7CH-402 (2" MPT) | Same |
| C-7400 | 7" × 14-3/4", 4 oz, 50 sq ft. Goldkey (one blue and one orange end cap) | 7CH-50 (1-1/2" MPT) or 7CH-502 (2" MPT) | Same |
| C-7449 | 7" × 14-3/4", 4 oz, 50 sq ft. Vita, Pleatco skim filter | 7CH-50 (1-1/2" MPT) | Remove the PAD adapter |
| 8CH-950 | 8" × 6", 2" SAE, 50 sq ft. Bullfrog (OEM 10-1035) | 8CH-951 | 8" × 5-3/4", 2" SAE. See our 8CH-950 page for the area ratings, which the sources print differently. |
| 8CH-60 | 8" × 11-5/8", 2" MPT, 60 sq ft. Continental | 8CH-66 | 8" × 9-1/4", 60 sq ft, shorter |
| 8CH-852AM | 85 sq ft antimicrobial. Diamante | 8CH-66 | Standard media, 60 sq ft |
| C-8320 | 8-7/16" × 18-1/8", castle top, 120 sq ft. Sundance | C-8325 | 8-7/16" × 18", 125 sq ft, Sundance universal length |
All rows are from the Unicel 2026 guide[5]. Where a cell says “price index”, the line comes from Unicel’s ordering list, not from the spec-table note.
Where Unicel’s two lists disagree
- C-5615 (Jacuzzi CFR-15). The spec note says use C-5625 (25 sq ft). The price index says use C-5635 (37 sq ft). Both have the same 5" × 13-5/16" body, so either fits the housing. They differ in area.
- C-6601. The spec note offers 6CH-35, 6CH-47 or 6CH-940. The index offers only 6CH-35 (MPT) or 6CH-940 (SAE).
- C-2612 (Rainbow 19X). The price index says “C-2612 USE C-2608” (12 sq ft to 8 sq ft, same 2-7/8" × 19-1/2" size). The spec table still prints C-2612 without a discontinued note.
- C-6430. The index says “C-6430 USE C-6430AM”, the antimicrobial version of the same Hot Spring / Watkins cartridge. See antimicrobial hot tub filters.
- Pool-size cartridges show the same pattern (C-7650, C-7487, C-8421: the spec note gives two choices and the index gives one).
When the lists disagree, both answers are the same diameter and length. Pick by the area and the fittings of your old cartridge, or ask your spa dealer which one the housing was rated for.
The PAD adapter step
Many old skim-filter cartridges were open-ended and screwed into the skimmer through a separate threaded PAD adapter. Their replacements are cartridges with the thread molded into the end cap. Unicel’s notes for C-4303, C-4324, C-6450, C-6475, C-7432, C-7439, C-7400 and C-7449 all say the threaded PAD adapter must be removed from the skim well, and they pick the replacement by the adapter’s thread: 1-1/2" MPT, 2" MPT, or SAE for C-6601[5]. Filbur gives the same instruction for its top-load cartridges: remove the PAD adapter, if installed, before threading the filter into the suction fitting. It also says independent testing found cartridges used with PAD adapters had lower flow than cartridges with integrated threads[31].
Before you unscrew the adapter, note its thread size (1-1/2" or 2"; MPT or SAE). That decides between 7CH-32 and 7CH-322, for example. Thread types are explained in open-end vs threaded hot tub filters.
Pleatco: deactivated spa numbers with a different replacement
Pleatco’s 2023 “Deactivated Pleatco part numbers” table includes these spa examples where the replacement is a different part, not just the same number with a suffix removed[2]:
| Deactivated | Pleatco replacement | Note |
|---|---|---|
| PRB37-IN, PRB37-IN-M | PRB50-IN | Rainbow in-line; replacement is the 50 sq ft cartridge |
| PFAB30 | PRB25-IN | |
| PCS32-2 (without adapter) | PAS35-F2M | |
| PJ200 | PJ150 | |
| PSD125-2006 | PSD125-2000 | Sundance |
| PDC510-AFS, PDC520-AFS, PDC530-AFS, PDC560-AFS, PDC100-AFS | PWK30, PRB35-IN, PLBS50, PLBS75, PRB75 | Dual-core cartridges replaced by standard ones |
| Microban -M numbers | Usually the same number without -M | Full list in antimicrobial hot tub filters |
Pleatco also lists some deactivated spa numbers with no replacement (“N/A”). Our Dimension One rows are examples: retailers still cross 1561-12, 1561-02 and 1561-10 to PDO75P3, PTL75XW-F2M and PTL55XW-F2M, which Pleatco lists as deactivated with no replacement[2]. For those, use the Unicel or Filbur number on the Dimension One lookup.
If your number is not on either list
- Search the number in the part-number search. It covers OEM, Unicel, Pleatco and Filbur numbers in our dataset.
- Try the other makers’ numbers printed on the end cap or the box. Our Filbur, Unicel and Pleatco number guide explains the prefixes.
- Measure diameter, length, the top and the bottom fitting, and use the size lookup. A different area rating at the same size is normal. See why same-size spa filters have different square feet.
Questions
What replaced the Unicel C-4303 spa filter?
Unicel says use 4CH-20 if the PAD adapter is MPT, and that the threaded PAD adapter must be removed from the skim well. The 4CH-20 is the same 4-5/8" × 6-3/4" size with a molded 1-1/2" MPT thread and is rated 20 sq ft against the C-4303’s 15.
What replaced the Bullfrog 8CH-950 filter?
Unicel lists 8CH-950 (OEM 10-1035) as discontinued and says use 8CH-951, an 8" × 5-3/4" cartridge with a 2" SAE thread.
What replaced the Sundance C-8320?
Unicel says use C-8325, the 8-7/16" Sundance universal-length cartridge rated 125 sq ft.
Is the C-5615 replaced by C-5625 or C-5635?
Unicel’s two lists disagree. The spec-table note says C-5625 (25 sq ft); the price index says C-5635 (37 sq ft). Both are 5" × 13-5/16" Jacuzzi in-line cartridges.
Why does the replacement filter have a different square footage?
Some replacements are rated differently even at the same size (C-4970 at 75 sq ft becomes C-4995 at 95), and a few are smaller (C-5302 at 50 sq ft becomes C-5624 at 25; C-6475 at 75 becomes the shorter 6CH-50 at 50). The catalog names the replacement; it does not promise the same rating.
Do I need to remove the PAD adapter when switching to a threaded cartridge?
Yes, according to both Unicel and Filbur. Unicel’s notes for the discontinued skim-filter cartridges say the threaded PAD adapter must be removed from the skim well, and Filbur says to remove it before threading its top-load cartridges into the suction fitting.
Sources
- Pleatco 2023 Catalog (Pentair)
- Unicel: Maintenance & FAQ
- Unicel 2026 Replacement Guide
- Filbur Catalog & Reference Guide
This guide summarizes published manufacturer and public-health guidance; always follow your own spa’s owner’s manual. See our disclaimer.