Which filter does my PDC spa take?

Reviewed November 7, 2026

Use the series and the year, then measure. PDC’s 2025 guide puts Luxury, Premium, SE and LX (1990 to present) on FLT-201TL, which it calls Unicel C-4326, 25 sq ft, about 5" × 13-5/16", open 2-1/8". LifeStyle, the XD2 spa side, and River (2010 to present) take FLT-171-CART, which PDC calls Unicel C-4405 at 25 sq ft. Unicel’s cross-reference and Filbur print that same C-4405 body at 50 sq ft for a two-cartridge set, and Pleatco prints 25 sq ft for one cartridge and 50 for the pair. Timeless and XTR (2000–2005) take FLT-118, Pleatco PRB7B, 17 sq ft. Pleatco’s 2023 list marks PRB7B deactivated and names no replacement. Nouveau (1996–1999) takes FLT-101SK, Pleatco PWW10. XD1, XD1+ and the XD2 cold side (2024 to present) take threaded FLT-1000-CART (Waterway 817-0020), not the open River cartridge. The XD2 name is on both. Swim spas Synergy, Summit, Splash and Vitality, and the hot-tub zone of dual-zone models (2009 to present), take FLT-SWIM50-CART (Unicel 4CH-949). TruSwim (2016 to present) takes FLT-SWIM75-CART (Unicel C-4975).

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The cartridges, with equivalents

The first column is PDC’s factory number from the 2025 guide. Square feet in that guide are PDC’s. Where Unicel, Pleatco or Filbur print a different area, length, opening or Unicel number, the conflict is in the tables below. Pleatco’s old PDC25-AFS, PDC100-AFS and PDC570-AFS numbers are deactivated catalog numbers. PDC’s 2025 guide does not print them, so they are not used as factory lookup numbers here.

The 2025 guide, series by series

PDC publishes one page, “Common Replacement Filter Elements,” created 26 March 2025. It says to order by the PDC part number, or by the manufacturer name and part number in the last column. It does not list individual spa model names inside Luxury, Premium, SE or LX. The assignment is the series and the year range.

XD2 is on two rows. The spa side of an XD2, from 2010 on, is the open 6-5/8" cartridge FLT-171-CART. The cold side of an XD2, from 2024 on, is the threaded 15 sq ft cartridge FLT-1000-CART. The series name does not finish the order. Look at the housing: an open cartridge about 6-5/8" long is the River row; a closed cartridge with a bar handle and a 1-1/2" SAE bottom, about 5-1/4" long, is the cold-side row.

Luxury, Premium, SE and LX: which Unicel number

PDC, Unicel’s PDC block and Pleatco agree that the long open 25 sq ft cartridge is C-4326 / PRB25-IN. They do not agree on the outside diameter. PDC prints 5". Unicel’s spec table prints 4-15/16" × 13-5/16", 2-1/8" open both ends, 106 pleats, 3 oz, 25 sq ft. Pleatco’s spec table prints PRB25-IN at 5" × 13-5/16", 2-1/8" open, 3 oz, 25 sq ft.

Filbur prints two different Unicel numbers for this size. The dimensional listing crosses FC-2375 to PRB25-IN and C-4326, 4-15/16" × 13-5/16", 2-1/8" open, 25 sq ft. The same listing crosses FC-2370 to PRB25-IN-4 and C-4625, the 4 oz cartridge of the same outside size. Unicel’s spec table prints C-4625 at 4-15/16" × 13-5/16", 106 pleats, 4 oz, 25 sq ft, and says the 37 sq ft C-4637 and the 50 sq ft C-4950 are upgrades of C-4326 and C-4625. Filbur’s PDC Spas section (printed p.45) does not print C-4326. It prints FC-2370 as Rainbow Dynamic 25, PRB25-IN-4, C-4325, 25 sq ft. C-4325 is a different cartridge in both catalogs: Filbur’s size table gives FC-1220, Hayward C-225, as C-4325 at 4-5/8" × 11-7/8". Do not order C-4325 for a Luxury, Premium, SE or LX spa because that cell says so. Hold the old cartridge against 13-5/16".

Same length, more area: Unicel calls C-4950 (50 sq ft, 212 pleats) an upgrade of this 25 sq ft body. PDC’s guide does not. Why the same size can carry two square-foot ratings is the pleat-count explanation. The Beachcomber C-4326 row is the same Unicel number for a different brand.

River, LifeStyle and the XD2 spa side: 25 or 50

PDC rates FLT-171-CART at 25 sq ft and names Unicel C-4405. Unicel’s PDC block does not list C-4405. Unicel’s spec table prints C-4405 at 4-15/16" × 6-5/8", 2-1/8" open both ends, 158 pleats, 4 oz, for Rainbow DSF-50 and Waterway, and the note says two cartridges per set with a stick handle. That spec row does not print a square-foot number. Unicel’s OEM cross-reference prints 50 in the square-foot column wherever it lists C-4405. Filbur’s dimensional listing prints FC-2387 at 4-15/16" × 6-5/8", 2-1/8" open, PRB25SF-PAIR/JH, C-4405, 50 sq ft, and the quantity column says “6 sets.”

Pleatco splits the number by the set. PRB25SF, one cartridge, is 5" × 6-5/8", 2-1/8" open, 3 oz, 25 sq ft. PRB25SF-PAIR and PRB25SF-JH-PAIR are the same body at 50 sq ft, and the cross-reference sends C-4405 to PRB25SF-JH-PAIR. PDC’s 25 sq ft matches the single. Unicel’s 50 and Filbur’s 50 match the pair. The guide does not say whether FLT-171-CART is sold as one cartridge or two. Measure the cartridge you removed. A dealer page that calls FLT-171-CART a two-pack is not the factory guide, so it is not used here as the count.

The Freedom C-4405 row and the Beachcomber pre-1995 set use this Unicel number for other brands. Filbur files neither of those under a PDC heading, and Filbur’s PDC section does not list FC-2387.

Timeless and XTR: a number Pleatco retired

PDC’s only manufacturer part for FLT-118 is Pleatco PRB7B, 17 sq ft, 5" × 4-5/8", 2-1/8" holes, for Timeless and XTR built from 2000 through 2005. Pleatco’s 2023 deactivated list prints PRB7B with replacement N/A. There is no PRB7B row in the 2023 spec table, so this site has no Pleatco diameter to put next to PDC’s 5".

Unicel’s PDC block lists a cartridge of that length and does not mention Timeless, XTR or FLT-118: C-4401, 35 sq ft, 4-15/16" × 4-5/8", 4 oz. The spec note says two cartridges per set. Filbur’s PDC section prints the same idea: FC-2386, 4-15/16" × 4-5/8", 2-1/8" open, Rainbow DSF 35, two per set, PRB17.5SF-PAIR/JH, C-4401, 35 sq ft. Pleatco’s current spec table prints PRB17.5SF-PAIR at 5" × 4-5/8", 35 sq ft, for Rainbow DSF 35. Pleatco does not say PRB7B was replaced by that pair. The areas are 17 (PDC, for PRB7B) and 35 (Unicel and Filbur, for C-4401). Order FLT-118 only if the cartridge in the spa matches 4-5/8" long and about 5" across, and read both areas before you treat C-4401 as the same part.

Nouveau, and the threaded XD cartridge

Nouveau, 1996–1999, is the small skim filter. PDC, Unicel and Pleatco agree: 10 sq ft, 4-1/4" × 4", openings 2-1/16". Unicel’s spec table prints C-4310 at 216 pleats, 3 oz. Pleatco prints PWW10 for Waterway Skim Filter 10, OEM 817-0010, at 3 oz and 10 sq ft, and a pair (PWW10PAIR) at 20 sq ft. PDC’s row is the single. Filbur’s dimensional listing and its PDC section both print FC-3077, PWW10, C-4310, 10 sq ft, 4-1/4" × 4", and both print the openings as 1-15/16", not 2-1/16". That is the only disagreement on this cartridge.

The 2024 XD cartridge is not an open skim filter. PDC says FLT-1000-CART is 15 sq ft, 4-5/8" × 5-1/4", a 1-1/2" SAE thread on the bottom, and a bar handle on a closed top, and it names Waterway 817-0020. Unicel’s Waterway line prints 817-0020 as 4CH-15: 15 sq ft, 4-5/8" × 5-3/16", dual bar handle, injection-molded 1-1/2" SAE, 199 pleats, 3 oz. The length differs by 1/16". Pleatco’s 2023 Unicel cross-reference has no 4CH-15 and no 817-0020. Filbur’s PDC section does not list it. Open-end versus threaded is the check: this one threads on. The Nouveau cartridge does not.

Swim spas: three lengths for one 50, and a 2" hole versus 2-1/8"

FLT-SWIM50-CART is PDC’s 50 sq ft top-mount for Synergy, Summit, Splash, Vitality, and the hot-tub zone of dual-zone models, from 2009 on. PDC prints 5" × 13-1/16" and a 1-1/2" female SAE bottom, which it also calls 38 mm, and it names Unicel 4CH-949. Unicel’s spec table prints 4CH-949 at 4-15/16" × 13-1/2", a v-groove handle, 210 pleats, 3 oz, 50 sq ft, and a 2" female SAE thread, with the note “For use on 1-1/2" male SAE stand pipe.” Pleatco’s spec table prints PWW50L at 5" × 13-3/16", a handle, 1-1/2" female SAE, 3 oz, 50 sq ft, Waterway Teleweir 50, OEM 817-4050. Unicel’s Waterway line also prints 817-4050 as 4CH-949. PDC does not print 817-4050. Filbur’s size table prints FC-0172 at 4-15/16" × 13-1/2", handle, 2" female SAE, 4CH-949, 50 sq ft. Three lengths (13-1/16", 13-3/16", 13-1/2") and two wordings of the thread (PDC and Pleatco say 1-1/2" female SAE; Unicel and Filbur say 2" female SAE, and Unicel adds that it goes on a 1-1/2" male standpipe). Measure the old cartridge. The Master Spas 4CH-949 row is the same Unicel number, with no PDC factory number.

TruSwim, 2016 to present, is FLT-SWIM75-CART. PDC prints 75 sq ft, 5" × 20-1/8", and a 2" center hole, and names Unicel C-4975. Unicel’s spec table prints C-4975 at 4-15/16" × 20-1/8", 2-1/8" open both ends, 210 pleats, 3 oz, 75 sq ft, Rainbow RTL-75. Pleatco prints PRB75 at 5" × 20-1/8", 2-1/8" both ends, 3 oz, 75 sq ft. Filbur’s size table prints FC-2395 at 4-15/16" × 20-1/8", 2-1/8" open, PRB75, C-4975, 75 sq ft. The length and the area agree. The opening is 2" on PDC’s page and 2-1/8" in Unicel, Pleatco and Filbur. The diameter is 5" or 4-15/16".

Two cartridges in the catalogs that the 2025 guide does not assign

Unicel’s PDC block also lists C-7626 (25 sq ft, 7" × 9-13/16", open with a molded gasket) and C-7656 (50 sq ft, 7" × 19-5/8", the same gasket). The spec table calls those Hayward CX250RE and CX500RE. Filbur’s PDC section prints them the same way: FC-1230, Hayward CX 250, C-7626, and FC-1240, Hayward CX 500, C-7656. PDC’s 2025 hot tub and swim spa guide does not name either part and does not give them a series. They are not given factory numbers on this page.

Where the sources disagree

• FLT-201TL’s Unicel number inside Filbur. PDC and Unicel’s PDC block: C-4326. Filbur’s size table: FC-2375 = C-4326, and FC-2370 = C-4625. Filbur’s PDC section: FC-2370 = C-4325. C-4325 is the 11-7/8" Hayward cartridge, not this 13-5/16" body.
• Outside diameter of the open 25 sq ft cartridge. Unicel and Filbur 4-15/16". PDC and Pleatco PRB25-IN 5".
• FLT-171-CART area. PDC 25 sq ft. Unicel’s cross-reference column and Filbur 50 sq ft, with a two-per-set note. Pleatco 25 for one cartridge and 50 for the pair.
• FLT-118. PDC names Pleatco PRB7B at 17 sq ft. Pleatco 2023: deactivated, replacement N/A. Unicel and Filbur list C-4401 at 35 sq ft and two per set for a cartridge of the same length, and they do not print PRB7B.
• Nouveau openings. PDC, Unicel and Pleatco 2-1/16". Filbur 1-15/16".
• XD length. PDC 5-1/4". Unicel 4CH-15 is 5-3/16".
• Swim 50 length. PDC 13-1/16". Pleatco 13-3/16". Unicel and Filbur 13-1/2".
• Swim 50 thread. PDC and Pleatco: 1-1/2" female SAE. Unicel and Filbur: 2" female SAE. Unicel’s note says the cartridge is for a 1-1/2" male SAE standpipe.
• TruSwim opening. PDC 2". Unicel, Pleatco and Filbur 2-1/8".
• What Filbur files under PDC. FC-3077, FC-2386, FC-2370, FC-1230 and FC-1240. Not C-4405, 4CH-15, 4CH-949 or C-4975.

How to confirm yours

1. Read the series off the spa, then the year if you have it. XD2 still needs the housing: spa side is FLT-171-CART, cold side from 2024 is FLT-1000-CART.
2. An open cartridge about 13-5/16" long is the Luxury / Premium / SE / LX row (FLT-201TL). About 6-5/8" long and open, it is the River row, and you still have to read 25 and 50 sq ft. About 4-5/8" long and open, it is the Timeless / XTR description, with PRB7B retired.
3. A closed cartridge with a bar handle and a 1-1/2" SAE bottom, about 5" long, is FLT-1000-CART. A 4-1/4" × 4" open cartridge is Nouveau.
4. A top-mount cartridge about 13" long with a female thread is the 50 sq ft swim filter. One about 20" long and open in the center is TruSwim. Compare the length you measure with 13-1/16", 13-3/16" and 13-1/2" before you order the 50.
5. The PDC Spas table has the sizes. How to measure a cartridge is the order of the measurements. Unicel’s length excludes a handle and includes the end caps.

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

Sources

1. PDC Spas: Common Replacement Filter Elements (one-page PDF, created 2025-03-26). Series, years, PDC part numbers, and the manufacturer part PDC names for each.
2. Unicel 2026 Replacement Guide: PDC Spas block, PDF p.47 (printed p.43): C-4310, C-4326, C-4401, C-7626, C-7656. No C-4405, 4CH-949, C-4975 or 817-0020 on that block.
3. Unicel 2026 Replacement Guide: spec table PDF p.6 (printed p.2), C-4310 and 4CH-15; PDF p.8 (printed p.4), C-4405, two per set; PDF p.9 (printed p.5), C-4326 (106 pleats, 25 sq ft), C-4625 (4 oz), C-4401 (two per set), 4CH-949 (2" female SAE, note for a 1-1/2" male SAE standpipe) and C-4975 (2-1/8" open, 75 sq ft).
4. Unicel 2026 Replacement Guide: Waterway Plastics line, 817-0020 = 4CH-15 (4-5/8" × 5-3/16", 15 sq ft, 1-1/2" SAE) and 817-4050 = 4CH-949.
5. Pleatco 2023 Catalog: spec table PDF p.31, PWW10 (4-1/4" × 4", 2-1/16", 10 sq ft) and PRB17.5SF-PAIR (5" × 4-5/8", 35 sq ft); PDF p.32, PRB25SF at 25 sq ft, PRB25SF-PAIR and PRB25SF-JH-PAIR at 50 sq ft, PRB25-IN (5" × 13-5/16", 25 sq ft), PWW50L (5" × 13-3/16", 1-1/2" female SAE, 50 sq ft) and PRB75 (5" × 20-1/8", 2-1/8", 75 sq ft).
6. Pleatco 2023 Catalog: Unicel cross-reference PDF p.47, C-4326 = PRB25-IN, C-4405 = PRB25SF-JH-PAIR, C-4310 = PWW10, 4CH-949 = PWW50L, C-4975 = PRB75. Deactivated list, PDF p.23: PRB7B replacement N/A. Deactivated list, PDF p.22: PDC25-AFS → PRB25-IN, PDC100-AFS → PRB75, PDC570-AFS → PWW50L. Those PDC-prefixed numbers are not in PDC’s 2025 guide.
7. Filbur Catalog: dimensional listing, PDF p.8 (printed p.15), FC-3077 = PWW10 = C-4310, 4-1/4" × 4", 1-15/16" open, 10 sq ft. PDF p.9 (printed p.16), FC-2387 = C-4405, 4-15/16" × 6-5/8", 2-1/8" open, 50 sq ft, 6 sets, with the note “2 cartridges per set with stick handle.” PDF p.9 (printed p.17): FC-2375 = PRB25-IN = C-4326, 25 sq ft; FC-2370 = PRB25-IN-4 = C-4625; FC-0172 = 4CH-949 at 13-1/2" with 2" female SAE; FC-2395 = C-4975.
8. Filbur Catalog: PDC Spas section, PDF p.23 (printed p.45). FC-3077 (Skim Filter 10, C-4310), FC-2386 (Rainbow DSF 35, two per set, C-4401), FC-2370 (Rainbow Dynamic 25, PRB25-IN-4, C-4325), FC-1230 (Hayward CX 250, C-7626), FC-1240 (Hayward CX 500, C-7656). No FLT part numbers, and no C-4405, 4CH-15, 4CH-949 or C-4975.

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