Which Waterway spa filter cartridge do I have?
The housing decides the part number, and the catalogs do not agree on the area. Waterway’s own table calls 817-0050 a 50 sq ft, 6" × 8-1/4" front-access cartridge. Unicel’s spec table prints that body, 6CH-940, at 45 sq ft, and Filbur’s sq ft column prints 40. A different front-access well does not take 817-0050: it stacks 817-0011 (upper, 1-3/4" male slip) on 817-0012 (lower, 1-1/2" SAE). The Teleweir cartridges are a third fitting, female SAE. 817-4025 and 817-4050 share a 13-1/2" length at 25 and 50 sq ft. 817-4035 is the shorter 35 sq ft Teleweir.
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The cartridges, with equivalents
| Factory part | What it is | Catalog equivalents | Rated area | Our page |
|---|---|---|---|---|
| 817-0050 | Front-access skim filter. One cartridge, or two side by side in the double-port housing. Same body either way. CMP’s number for this cartridge, on Unicel’s other list, is 25252. | Unicel 6CH-940. Pleatco PWW50P3. Filbur FC-0359. | 6" × 8-1/4", handle, 1-1/2" SAE, 225 pleats. Spec table 45 sq ft. Waterway’s table and Unicel’s Waterway line: 50. Filbur’s column: 40. Pleatco’s length is 7-5/8". | 6CH-940 |
| 817-0011 | Upper cartridge of the stacked front-access pair. 1-3/4" male slip on the bottom. Does not replace 817-0050. | Unicel 6CH-941. Filbur FC-0360. Pleatco’s live number is the set PWW100P3-SET, not a single cartridge. | 6" × 8-1/4", 225 pleats. Spec table 45 sq ft. Waterway’s table: 50 sq ft upper. Filbur’s description says 40; its Waterway column prints 80. | 6CH-941 |
| 817-0012 | Lower cartridge of that stack. 1-3/4" open top, 1-1/2" SAE bottom. Unicel says it must be used with 6CH-941. | Unicel 6CH-942. Filbur FC-0361. Same Pleatco set, PWW100P3-SET. | 6" × 8-1/4", 225 pleats. Same 45 / 50 / 40 split as the upper. | 6CH-942 |
| 817-4025 | Teleweir skim filter, 25 sq ft. Same length as the 50 sq ft Teleweir. The thread is female SAE, not the front-access 1-1/2" SAE. | Unicel 4CH-926. Pleatco PWW25L (cross-reference). Filbur FC-0168. | Unicel and Waterway: 4-15/16" × 13-1/2", 25 sq ft, 2" female SAE. Pleatco: 5" × 13-3/16". Filbur’s length: 13-1/16". | 4CH-926 |
| 817-4035 | Teleweir skim filter, the short one. Nordic sells this Waterway number as CARTRIDGE-T35. | Unicel 4CH-935. Pleatco PWW35L. Filbur’s Waterway row is FC-0170 and prints Unicel N/A. | Unicel and Waterway: 4-15/16" × 9-1/4", 35 sq ft. Pleatco: 5" × 8-1/2", 35 sq ft. Filbur’s Waterway row: 30 sq ft. | 4CH-935, 4CH-935 |
| 817-4050 | Teleweir skim filter, 50 sq ft. Same 13-1/2" body as 817-4025, twice the area. | Unicel 4CH-949. Pleatco PWW50L. Filbur FC-0172 (Rising Dragon section; that row does not print 817-4050). | Unicel and Waterway: 4-15/16" × 13-1/2", 50 sq ft, 2" female SAE. Pleatco: 5" × 13-3/16", 1-1/2" female SAE. | 4CH-949 |
| 817-0010 | 10 sq ft skim filter. Open both ends. Not a front-access cartridge. | Unicel C-4310. Pleatco PWW10. Filbur FC-3077. | 4-1/4" × 4", open 2-1/16" (Unicel and Pleatco). Filbur prints the top opening as 1-15/16". 10 sq ft. Pleatco’s pair, PWW10PAIR, is 20 sq ft. | C-4310 |
| 817-2500 | 25 sq ft top-load, in-line. The open 4-15/16" × 13-5/16" body, not a Teleweir. | Unicel C-4326. Pleatco PRB25-IN. Filbur lists it twice: FC-2375 and FC-2910. | Unicel: 4-15/16" × 13-5/16", open 2-1/8", 25 sq ft. Pleatco’s outside diameter is 5". Filbur’s two rows print 13-5/16" and, for FC-2910, 12-1/4" in the Waterway section and 13-1/4" in the size table. | C-4326 |
| 817-5000 | 50 sq ft top-load, in-line. Same outside size as 817-2500. | Unicel C-4950. Pleatco PRB50-IN. Filbur FC-2390. | 4-15/16" × 13-5/16", open, 50 sq ft in Unicel and Filbur. Pleatco prints 5" outside diameter. | C-4950 |
| 817-7500 | 75 sq ft top-load. Unicel says this cartridge, C-4970, is discontinued. Waterway’s current table still lists 817-7500 at 75 sq ft. | Unicel C-4970, with the note to use C-4995. Filbur FC-2930 still prints C-4970. Pleatco deactivates PCAL75 and sends it to PCAL100. | 4-15/16" × 23-5/8", open, 75 sq ft. The replacement Unicel names is the 95 sq ft cartridge, not another 75. | C-4970 |
| 817-1000 | The long top-load Unicel tells you to use instead of 817-7500. The area is not the same number in every list. | Unicel C-4995. Pleatco PCAL100. Filbur FC-2940. | 4-15/16" × 23-5/8". Unicel spec and the Waterway OEM line: 95 sq ft. Waterway’s table, Pleatco, and Filbur’s Waterway section: 100 sq ft. Pleatco’s outside diameter is 5". | C-4995 |
| 817-0018 | Dyna-Flo XL, 75 sq ft. Waterway prints three dimensions: 2-3/8" × 6-9/16" × 13-5/16". The 2-3/8" is the open end. | Unicel C-6375. Filbur FC-3754. No Pleatco number in the 2023 cross-reference. | 6-9/16" × 13-5/16", open 2-3/8", 75 sq ft. Unicel, Filbur, and Waterway’s table agree. | C-6375 |
Square feet in the “Rated area” column are the figure Unicel’s spec table prints for one cartridge, except where the row says otherwise. Waterway’s table and Unicel’s Waterway list often print 50 where the spec table prints 45. A 100 or 200 on Unicel’s Waterway list is the housing total, not a longer cartridge. Pool cartridges on the same Waterway table (ProClean, Clearwater, inground) are not on this page.
Front access: one cartridge, two side by side, or a stack
Waterway’s table, fetched 2026-11-09, calls 817-0050 “50SF Filter Cartridge 6″ × 8-1/4″ F/A Skimmer,” 817-0011 “50 SQ.FT. Upper Cartridge (Extension),” and 817-0012 “50 SQ.FT. Lower Cartridge (Extension).”
| Housing | What goes in it | What the sources print |
|---|---|---|
| Single-port front access | One 817-0050 (Unicel 6CH-940, Pleatco PWW50P3, Filbur FC-0359). CMP 25252 is the same Unicel cartridge. | Waterway and Unicel’s Waterway line: 50 sq ft, 6" × 8-1/4", 1-1/2" SAE. Unicel’s spec table and Unicel’s own product list: 45 sq ft, 225 pleats. Filbur’s sq ft column: 40. Pleatco: 50 sq ft at 6" × 7-5/8", and “2 required.” |
| Double-port front access | Two 817-0050, side by side. Unicel prints this as 100 sq ft on a second 817-0050 line. | Unicel’s note is “Two 50 sq.ft. cartridges required.” Filbur’s Waterway row also says two are used side by side, and it calls each one 40 sq ft. Nobody prints 90, which is what two of the spec-table 45 would be. |
| Stacked front access | 817-0011 on top of 817-0012. Unicel: 6CH-941 must be used with 6CH-942. Each is 6" × 8-1/4". | Waterway: 50 sq ft each. Unicel spec: 45 each, 225 pleats. The upper bottom is a 1-3/4" male slip. The lower top is a 1-3/4" open, and the lower bottom is 1-1/2" SAE. Pleatco sells the pair as PWW100P3-SET, 6" × 16-1/2", 100 sq ft, OEM 817-0011 / 817-0012 (and CMP 25253 / 25254). Two 7-5/8" cartridges would not add to 16-1/2". |
| Double-port stack | Two uppers and two lowers. Unicel prints 200 sq ft. | Unicel’s note: two 817-0011 and two 817-0012. That is four cartridges, not one 200 sq ft cartridge. |
A 1-1/2" SAE bottom and a 1-3/4" slip bottom do not interchange. The open-versus-threaded check is in open-end vs threaded filters. Counting a side-by-side pair against a spare set is in spas that use more than one filter.
Teleweir: same length, two areas, and a shorter third
Unicel’s note on the Teleweir spec lines is “For use on 1-1/2" male SAE stand pipe,” under a 2" female SAE bottom. Pleatco prints the bottom as 1-1/2" female SAE. Order by the number, then hold the new cartridge against the old one.
| Waterway | Unicel | Waterway’s table | Pleatco | Filbur |
|---|---|---|---|---|
| 817-4025 | 4CH-926, 4-15/16" × 13-1/2", 105 pleats, 25 sq ft, 2" female SAE | 25 sq ft, 4-15/16" × 13-1/2", SAE | PWW25L, 5" × 13-3/16", 25 sq ft. The spec line does not print 817-4025. The cross-reference does: 4CH-926 = PWW25L. | FC-0168, 4-15/16" × 13-1/16", 1-1/2" female SAE, 25 sq ft. The size table does not print 817-4025. |
| 817-4035 | 4CH-935, 4-15/16" × 9-1/4", 219 pleats, 35 sq ft, 2" female SAE | 35 sq ft, 4-15/16" × 9-1/4", SAE | PWW35L, 5" × 8-1/2", 35 sq ft, OEM 817-4035 | Waterway section: FC-0170, 4-15/16" × 9-1/4", 30 sq ft, Unicel N/A, OEM 817-4035 |
| 817-4050 | 4CH-949, 4-15/16" × 13-1/2", 210 pleats, 50 sq ft, 2" female SAE | 50 sq ft, 4-15/16" × 13-1/2", SAE | PWW50L, 5" × 13-3/16", 50 sq ft, OEM 817-4050, 1-1/2" female SAE | FC-0172, 4-15/16" × 13-1/2", 2" female SAE, 50 sq ft, under Rising Dragon. That row does not print 817-4050. |
817-4025 and 817-4050 are the same length. The area is the difference, which is the pleat-count split in why the same size can carry two square-foot ratings. Nordic’s chart uses 817-4035 as CARTRIDGE-T35; that model list is on the Nordic filter page. PDC’s swim-spa cartridge is the 4CH-949 body and does not print 817-4050; see PDC by series.
Top-load numbers, including the discontinued 75
Unicel’s note at the top of the Waterway list says originals had teal end caps from 2003 to 2006. Waterway’s current table does not say that. It does not change which number fits.
817-2500 and 817-5000 are the open 25 and 50 sq ft cartridges, both about 4-15/16" × 13-5/16". Unicel calls the 50 an upgrade of the 25: more pleats, same length. Pleatco prints both at 5" outside diameter. Filbur files 817-2500 on two rows, FC-2375 at 13-5/16" (Pleatco PRB25-IN) and FC-2910, which the size table lengths at 13-1/4" and the Waterway section lengths at 12-1/4", with no Pleatco number.
817-7500 is Unicel C-4970, 75 sq ft, 4-15/16" × 23-5/8". Unicel says C-4970 is discontinued and to use C-4995. C-4995 is 817-1000, and Unicel rates that cartridge at 95 sq ft, not 75. Pleatco’s deactivated list sends PCAL75 to PCAL100, and the PCAL100 spec is 5" × 23-5/8", 100 sq ft, OEM 817-1000. Waterway’s table still lists 817-7500 at 75 sq ft and 817-1000 at 100. Filbur’s Waterway section still prints FC-2930 as C-4970 at 75, and FC-2940 as C-4995 at 100. A later Filbur size row prints that same FC-2940 at 95. The replacement is not the same area as the cartridge it replaces. That pattern is the subject of discontinued spa filter numbers.
817-0018, the 75 sq ft Dyna-Flo XL, is the row the three sources agree on: 6-9/16" × 13-5/16", open 2-3/8", 75 sq ft. Waterway writes the open end first (2-3/8" × 6-9/16" × 13-5/16"). Unicel’s spec table and Filbur FC-3754 print the same three numbers. The 2023 Pleatco cross-reference has no C-6375 line.
Unicel also lists 817-0020 (the 15 sq ft 4CH-15, already on the PDC XD cartridge), 817-3501 (C-4335, which Waterway’s table calls an F/A skim filter and Unicel calls a top-load), 817-0040 (C-4339), and the short pairs 817-3510 (C-4401, two per set) and 817-5010 (C-4405, two per set). Those open bodies already have cartridge pages under other brands. This page does not add a second copy of them. The inground, ProClean, and Clearwater pool cartridges on Waterway’s table are a different product line and are not listed here.
Where the sources disagree
- 817-0050 area. Waterway’s table and Unicel’s Waterway line: 50 sq ft. Unicel’s spec table and Unicel’s product list: 45. Filbur’s sq ft column: 40. Pleatco: 50, at 7-5/8" long instead of 8-1/4".
- 817-0011 / 817-0012 area. Waterway: 50 each. Unicel spec: 45 each. Filbur’s description: 40 each. Filbur’s Waterway sq ft column on those two rows: 80. Pleatco’s set: 100 sq ft at 16-1/2" for the pair.
- Teleweir length and thread. 817-4025 is 13-1/2" (Unicel, Waterway), 13-3/16" (Pleatco), or 13-1/16" (Filbur). The female thread is 2" in Unicel and 1-1/2" in Pleatco and in Filbur’s 817-4025 size row. 817-4035 is 9-1/4" and 35 sq ft in Unicel and on Waterway’s table, 8-1/2" and 35 in Pleatco, and 9-1/4" and 30 in Filbur, which prints no Unicel number.
- 817-2500 length inside Filbur. FC-2375 is 13-5/16". FC-2910 is 13-1/4" in the size table and 12-1/4" in the Waterway section. Unicel and Pleatco print 13-5/16".
- 817-7500 and 817-1000. Unicel discontinues the 75 and names a 95 sq ft replacement. Waterway still sells both, at 75 and 100. Pleatco sends PCAL75 to PCAL100 and rates PCAL100 at 100. Filbur prints 75 for the old number and both 100 and 95 for the new one.
How to confirm yours
- Read the 817- number on the end cap. 817-0050, 817-0011, and 817-0012 are three cartridges. The first does not stack on the other two.
- If the bottom is a female SAE and the body is about 5" across, you are on a Teleweir. Length about 13-1/2" is 817-4025 or 817-4050. Length about 9" is 817-4035. The area, not the length, splits the two long ones.
- If both ends are open and the body is about 5" × 13", you are on 817-2500 (25 sq ft) or 817-5000 (50 sq ft), not a Teleweir.
- If the number is 817-7500, Unicel’s current replacement is 817-1000, and that cartridge is 95 or 100 sq ft depending on which list you read. It is not a 75.
Why one cartridge size can carry two different square-foot ratings: our explainer with Unicel’s pleat-count table.
Sources
- Waterway Plastics, Service Logic replacement-cartridge table, “Skimmer and skim filter options,” fetched 2026-11-09: 817-0010, 817-0011, 817-0012, 817-0018, 817-0050, 817-1000, 817-2500, 817-3501, 817-3510, 817-4025, 817-4035, 817-4050, 817-5000, 817-7500, with the descriptions quoted on this page
- Unicel 2026 Replacement Guide, Waterway Plastics OEM list, PDF pp.64–65 (printed pp.60–61): the teal end-cap note for 2003–2006, the Teleweir rows, the front-access rows and the side-by-side and stacked counts, 817-7500 discontinued in favor of C-4995, and 817-0018
- Unicel 2026 Replacement Guide, spec table: 6CH-940, 6CH-941, and 6CH-942 at 45 sq ft, 6" × 8-1/4", 225 pleats, PDF p.12 (printed p.8); 4CH-926 and 4CH-949, PDF p.9 (printed p.5); 4CH-935, PDF p.8 (printed p.4); C-4310, PDF p.6 (printed p.2); C-4970 and C-4995, PDF p.9; C-6375, PDF p.13 (printed p.9). The generic Unicel product list, PDF p.61 (printed p.57), also prints the three front-access cartridges at 45 sq ft.
- Pleatco 2023 Catalog, spec table PDF pp.32–33: PWW25L, PWW35L (OEM 817-4035), PWW50L (OEM 817-4050), PWW50P3 (OEM 817-0050, 6" × 7-5/8", 50 sq ft, “2 required”), PWW100P3-SET (6" × 16-1/2", 100 sq ft, OEM 817-0011 / 817-0012), PWW10 (OEM 817-0010), PRB25-IN and PRB50-IN (OEM 817-2500 and 817-5000), PCAL100 (OEM 817-1000, 100 sq ft). Cross-reference PDF p.47: 4CH-926 = PWW25L, 4CH-935 = PWW35L, 4CH-949 = PWW50L, 6CH-940 = PWW50P3, 6CH-941 and 6CH-942 = PWW100P3-SET, C-4310 = PWW10, C-4995 = PCAL100. Deactivated list PDF p.21: PCAL75 replacement PCAL100.
- Filbur Catalog, Waterway Plastics section, PDF pp.28–29: FC-0359 / 817-0050 at 40 sq ft with two cartridges side by side; FC-0360 / 817-0011 and FC-0361 / 817-0012; FC-0170 / 817-4035 at 30 sq ft with Unicel N/A; FC-2910 and FC-2375 both for 817-2500; FC-2930 / 817-7500 still as C-4970 at 75; FC-2940 / 817-1000 at 100; FC-3754 / 817-0018. Dimensional listing: FC-0168 at 13-1/16" for 4CH-926; FC-2910 at 13-1/4"; a later FC-2940 row at 95 sq ft.
This page summarizes published catalogs and dealer fitment tables; always follow your own spa’s owner’s manual. See our disclaimer and methodology.