PWK35B / C-6350 / FC-3921
35 sq ft replacement filter cartridge • 6.375″ OD × 14″ long
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Use the part-number links below to compare compatible cartridges. Prices and availability vary, so verify dimensions before ordering.
Cross-Reference & Interchangeable Part Numbers
| Brand | Part Number | Type |
|---|---|---|
| Pleatco | PWK35B | Primary |
| Unicel | C-6350 | Equivalent |
| Filbur | FC-3921 | Equivalent |
| OEM | Watkins 78161 | Original Equipment |
| OEM | Watkins 78286 | Original Equipment |
| OEM | Watkins 1642301-1 | Original Equipment |
Always verify dimensions and end-cap type before purchasing a replacement.
Compatible Hot Tubs & Spas
The following spa models use the PWK35B (or an interchangeable equivalent). Always confirm with your owner's manual.
| Brand | Model |
|---|---|
| Hot Spring | Limelight Pulse |
| Hot Spring | Limelight Flair |
| Hot Spring | Limelight Flash |
| Hot Spring | Limelight Beam |
Frequently Asked Questions
What are the dimensions of the PWK35B?
The PWK35B measures 6.375 inches in outer diameter and 14 inches in length, with a open top and open bottom. It provides 35 square feet of filtration area. Always measure your existing cartridge or check the label inside the filter housing before ordering - outer diameter and length are the two critical dimensions, but end-cap style must also match.
What other part numbers are interchangeable with the PWK35B?
The PWK35B is interchangeable with C-6350, FC-3921, and OEM equivalents including Watkins 78161, Watkins 78286, Watkins 1642301-1. All of these share the same 6.375" OD × 14" dimensions and open top / open bottom end caps. When buying a cross-reference, confirm the end-cap style matches - a small difference in cap design can prevent proper seating in your filter housing.
How often should I replace a PWK35B filter cartridge?
The PWK35B (35 sq ft) is a mid-size spa filter. Plan on 12-24 months between replacements depending on how heavily the spa is used. Spas used daily or by multiple people will wear out filters faster than a spa used once or twice a week. A good rule of thumb: inspect it at every water change (every 3-4 months) and replace it when the pleats show tearing, channeling, or persistent discoloration.
How do I clean a PWK35B filter cartridge?
The PWK35B has open ends on both top and bottom, so water flows through freely. Remove the cartridge from its housing and rinse thoroughly with a garden hose, directing the stream at a 45-degree angle between the pleats - work from top to bottom, rotating around the cartridge. Avoid pressure washers, which collapse the pleats and permanently reduce filtration efficiency. For a deeper clean every 3-4 months, soak overnight in a hot tub filter cleaner solution, then rinse thoroughly. Never reinstall a wet cartridge if you're using a cartridge with a closed end - let it dry to prevent trapping moisture inside.
Which hot tubs and spas use the PWK35B filter?
The PWK35B is compatible with the following models: Hot Spring Limelight Pulse, Hot Spring Limelight Flair, Hot Spring Limelight Flash, Hot Spring Limelight Beam. Always cross-check your spa's owner manual or the label inside the filter compartment to confirm the correct part number.
Dimensions
Specifications
| Outer Diameter | 6.375″ |
|---|---|
| Length | 14″ |
| Top Type | Open (no end cap) |
| Bottom Type | Open (no end cap) |
| Filtration Area | 35 sq ft |
| Primary Brand | Pleatco |
| Part Number | PWK35B |