Softub spa filter (4CH-20)

Softub Unverified: single source (Unicel only); no OEM part number; no Pleatco equivalent; no Filbur equivalent; no model/model-year fitment in sources. Checked 2026-10-31: Softub's 2025 owner's manual and Softub dealers (SoftubDirect, SpaStore, Simply Spas, ezhottubparts) describe snap-on 5020/5015/5010 filters, and the threaded replacement SoftubDirect sells is 4CH-23DF; retailer tables that list 4CH-20 for Softub repeat the Unicel size with no OEM number. Checked 2026-11-03: Hot Tub Essentials (ProAqua 4CH-20) and Hot Tub Outpost (ProLine P4CH-20) list Softub among the brands for this size with no Softub OEM number, in wording that matches Unicel's own listing; not an independent source. Checked 2026-11-04: Filbur lists FC-0125 / 4CH-20 under Saratoga (that row prints 15 sq ft), Leisure Bay (20 sq ft), Softsider (20 sq ft) and Vita (25 sq ft, OEM PVT-25), not under Softub. Pleatco lists Unicel's Saratoga OEM 20241-238 as PSG25P4 at 25 sq ft, not as a Softub part. Still no second source for the Softub application. Checked 2026-11-06: a pass over the Filbur catalog PDF found no row that prints Softub next to FC-0125 / 4CH-20. The size table still prints that Filbur number at 20 sq ft (Pleatco cell PHC25), and one brand row still prints Vita OEM PVT-25 at 25 sq ft. Checked 2026-11-07: Filbur still does not print Softub on an FC-0125 / 4CH-20 row. A Filbur brand row still pairs 4CH-20 with Vita OEM PVT-25. Still unresolved. Checked 2026-11-08: Unicel's Softub section still lists only this 20 sq ft 4-5/8" x 6-3/4" 1-1/2" MPT cartridge, with no OEM. Pleatco's Softub spec line is PTL20W-SV-P4 for OEM 90-802, not 4CH-20. Filbur's text contains no Softub. Still unresolved.

Replacement numbers

Unicel 4CH-20

Fits Softub.

Diameter 4-5/8" (117 mm)Length 6-3/4" (171 mm)20 sq ft

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Unicel4CH-20
Pleatconot found in source
Filburnot found in Filbur catalog
Topmolded cone handle
Bottom1-1/2” male thread/MPT
Ø 4-5/8" (117 mm)6-3/4" (171 mm)Side view · end views belowTopBottom
Top: molded cone handle
Bottom: 1-1/2” male thread/MPT
Drawn to scale from the listed diameter and length. Handles, threads and closed ends are drawn as symbols, not to scale. 20 sq ft media.

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For Softub, 4CH-20 cartridge sits in Softub. The cross-reference prints Unicel 4CH-20. 4-5/8" across, 6-3/4" long, top molded cone handle, bottom 1-1/2” male thread/MPT, 20 sq ft.

4CH-20 carries this note from the catalogs: Unicel lists this 4-5/8" x 6-3/4" top-load cartridge for Softub. No OEM number is given, and neither Pleatco nor Filbur mentions Softub for it.

4CH-20 is easy to confuse on the Softub table. 6CH-25 differs by Unicel 6CH-25, Pleatco PTL20W-SV-P4, Filbur FC-0305, 6" diameter, 5-1/2" long, top semi-circular handle, 25 sq ft, OEM 90-802, note says Unicel rates 6CH-25 at 25 sq ft; Pleatco rates PTL20W-SV-P4 (same OEM 90-802, 6" x 5-1/2", handle, 1-1/2" MPT) at 20 sq ft. The Filbur catalog lists FC-0305 against the same OEM 90-802 at 6" x 5-1/2", handle top, 1-1/2" MPT, 25 sq ft, and cross-references it to PTL20W-SV-P-4 and 6CH-25. Size, OEM number and fitting agree across all three catalogs..

Pleatco and Filbur do not have a number on this row. Search 4CH-20 or the Softub part you pulled out of the spa.

Left blank on purpose: single source (Unicel only); no OEM part number; no Pleatco equivalent; no Filbur equivalent; no model/model-year fitment in sources. Checked 2026-10-31: Softub's 2025 owner's manual and Softub dealers (SoftubDirect, SpaStore, Simply Spas, ezhottubparts) describe snap-on 5020/5015/5010 filters, and the threaded replacement SoftubDirect sells is 4CH-23DF; retailer tables that list 4CH-20 for Softub repeat the Unicel size with no OEM number. Checked 2026-11-03: Hot Tub Essentials (ProAqua 4CH-20) and Hot Tub Outpost (ProLine P4CH-20) list Softub among the brands for this size with no Softub OEM number, in wording that matches Unicel's own listing; not an independent source. Checked 2026-11-04: Filbur lists FC-0125 / 4CH-20 under Saratoga (that row prints 15 sq ft), Leisure Bay (20 sq ft), Softsider (20 sq ft) and Vita (25 sq ft, OEM PVT-25), not under Softub. Pleatco lists Unicel's Saratoga OEM 20241-238 as PSG25P4 at 25 sq ft, not as a Softub part. Still no second source for the Softub application. Checked 2026-11-06: a pass over the Filbur catalog PDF found no row that prints Softub next to FC-0125 / 4CH-20. The size table still prints that Filbur number at 20 sq ft (Pleatco cell PHC25), and one brand row still prints Vita OEM PVT-25 at 25 sq ft. Checked 2026-11-07: Filbur still does not print Softub on an FC-0125 / 4CH-20 row. A Filbur brand row still pairs 4CH-20 with Vita OEM PVT-25. Still unresolved. Checked 2026-11-08: Unicel's Softub section still lists only this 20 sq ft 4-5/8" x 6-3/4" 1-1/2" MPT cartridge, with no OEM. Pleatco's Softub spec line is PTL20W-SV-P4 for OEM 90-802, not 4CH-20. Filbur's text contains no Softub. Still unresolved..

Where those figures are printed: Unicel 2026 Replacement Guide on 4CH-20 (OEM cross reference (Softub section), PDF p.55 (printed p.51); spec table PDF p.7 (printed p.3)).

If you know the Softub model and not the part number, use the Softub filter by model and year lookup.

Check the cartridge you removed

Measure diameter, length, and both ends, then compare them with the figures above. The steps are in the measuring guide. Why the bottom decides whether it seals: open-end vs threaded filters. Power, the retainer, and not running the spa empty: how to install a cartridge. Number formats: how Filbur, Unicel and Pleatco numbers compare.

The same 4CH-20 number is also on the Saratoga Spas page.

Other Softub cartridges

All 2 Softub spa filters

Every number on this row, on one screen: cross-reference lookup. Published clean and replace intervals for this cartridge, and a buy link for the numbers above: replacement schedule and reorder. The interval comparison by brand: calculator.

Cleaner and test strips

Hose rinse and soak steps are in how to clean a cartridge. Named cleaners and strips are in filter cleaners and test strips.

Filter cleaner and test strips

Unverified. This row has not been fully confirmed against a second source. Gaps: single source (Unicel only); no OEM part number; no Pleatco equivalent; no Filbur equivalent; no model/model-year fitment in sources. Checked 2026-10-31: Softub's 2025 owner's manual and Softub dealers (SoftubDirect, SpaStore, Simply Spas, ezhottubparts) describe snap-on 5020/5015/5010 filters, and the threaded replacement SoftubDirect sells is 4CH-23DF; retailer tables that list 4CH-20 for Softub repeat the Unicel size with no OEM number. Checked 2026-11-03: Hot Tub Essentials (ProAqua 4CH-20) and Hot Tub Outpost (ProLine P4CH-20) list Softub among the brands for this size with no Softub OEM number, in wording that matches Unicel's own listing; not an independent source. Checked 2026-11-04: Filbur lists FC-0125 / 4CH-20 under Saratoga (that row prints 15 sq ft), Leisure Bay (20 sq ft), Softsider (20 sq ft) and Vita (25 sq ft, OEM PVT-25), not under Softub. Pleatco lists Unicel's Saratoga OEM 20241-238 as PSG25P4 at 25 sq ft, not as a Softub part. Still no second source for the Softub application. Checked 2026-11-06: a pass over the Filbur catalog PDF found no row that prints Softub next to FC-0125 / 4CH-20. The size table still prints that Filbur number at 20 sq ft (Pleatco cell PHC25), and one brand row still prints Vita OEM PVT-25 at 25 sq ft. Checked 2026-11-07: Filbur still does not print Softub on an FC-0125 / 4CH-20 row. A Filbur brand row still pairs 4CH-20 with Vita OEM PVT-25. Still unresolved. Checked 2026-11-08: Unicel's Softub section still lists only this 20 sq ft 4-5/8" x 6-3/4" 1-1/2" MPT cartridge, with no OEM. Pleatco's Softub spec line is PTL20W-SV-P4 for OEM 90-802, not 4CH-20. Filbur's text contains no Softub. Still unresolved.. Measure your old cartridge before ordering.

Sources