PWK65 / C-8465 / FC-3960
65 sq ft replacement filter cartridge • 8.5″ OD × 10.5″ long
Short and wide sums up the PWK65: 8-1/2 inches in diameter but only 10-1/2 inches tall, with 3-inch openings top and bottom. It's the cartridge for Hot Spring's Tiger River tubs (the Phoenix, Bengal, Caspian, and Sumatran) and for the first-generation Limelight models built between 2008 and 2017. It even goes back to the 1989-1990 Highlife Classic. Watkins numbers include 31114, 71827, and 71828, and it also carries the Caldera 76136 number. The cross-references are Unicel C-8465 and Filbur FC-3960. Because the diameter is so large, you can't eyeball this one against a standard spa filter. Check that stubby 8-1/2-inch width against your housing first.
Compare on Amazon
PWK65 replacements on Amazon
The buttons below pull up Amazon results for each cross-reference part number. Same physical cartridge, different stickers, often different prices. Cross-shop and pick the cheapest option that has solid recent reviews.
Cross-Reference & Interchangeable Part Numbers
| Brand | Part Number | Type |
|---|---|---|
| Pleatco | PWK65 | Primary |
| Unicel | C-8465 | Equivalent |
| Filbur | FC-3960 | Equivalent |
| OEM | Watkins 31114 | Original Equipment |
| OEM | Watkins 71827 | Original Equipment |
| OEM | Watkins 71828 | Original Equipment |
| OEM | Caldera 76136 | Original Equipment |
Always verify dimensions and end-cap type before purchasing a replacement.
Compatible Hot Tubs & Spas
The PWK65 (or any of its cross-references) fits these spa models. Cartridge sizing occasionally shifted between model years, so it's worth confirming against your owner's manual or the cartridge label.
| Brand | Model |
|---|---|
| Hot Spring | Tiger River Phoenix |
| Hot Spring | Tiger River Bengal |
| Hot Spring | Tiger River Caspian |
| Hot Spring | Tiger River Sumatran |
| Hot Spring | Limelight Bolt |
| Hot Spring | Limelight Glow |
Frequently Asked Questions
What are the dimensions of the PWK65?
The PWK65 is 8.5 inches in outer diameter, 10.5 inches long, with an open top and an open bottom. Total filtration area is 65 square feet. Before ordering, pull your existing cartridge and measure it yourself, or check the label inside the housing. OD and length both have to match within about an eighth of an inch, and the end-cap style needs to match exactly so the cartridge seats properly when the lid closes.
What other part numbers are interchangeable with the PWK65?
PWK65 is the same physical cartridge as C-8465, FC-3960, plus OEM versions like Watkins 31114, Watkins 71827, Watkins 71828, Caldera 76136. Same dimensions (8.5" × 10.5"), same open top, same open bottom. The Pleatco, Unicel, and Filbur boxes ship the same media inside, just with different stickers. The only thing to watch is the end-cap style: if a cross-reference has a slightly different cap design, it may not seat right in your housing.
Is the Watkins 31114 the same filter as the PWK65?
Yes. Watkins 31114 is an OEM number, the code the tub or pool builder stamps on the cartridge they ship. The filter itself is made by Pleatco, Unicel, or Filbur, so Watkins 31114 (along with Watkins 71827, Watkins 71828, Caldera 76136) and PWK65, C-8465, FC-3960 all point to one interchangeable cartridge. Buy whichever is cheapest with solid recent reviews, and just check that the dimensions match your old cartridge before you order.
How often should I replace the PWK65?
Mid-size spa cartridges like the PWK65 (65 sq ft) usually last 12 to 24 months. It shows up most often in Hot Spring tubs. The real driver is use: a tub that gets daily soaks for a couple of people burns through cartridges about twice as fast as one used a few times a month. A good rhythm is a monthly hose rinse, a deep soak in cleaner at every water change (every three to four months), and replacement once the pleats tear, the seams stain brown, or a soak no longer brings post-clean pressure back to baseline.
How do I clean the PWK65?
The PWK65 has open ends on both top and bottom, so water flows straight through. Pull the cartridge from the housing and hose it down. Hit the pleats from above at about a 45-degree angle so water rinses debris out instead of packing it deeper, and work top to bottom while rotating the cartridge. Skip the pressure washer. The high pressure tears or collapses pleats, and once that happens you've lost media that doesn't come back. Every few months (or at every water change, whichever comes first), do a deep clean: overnight soak in a hot tub filter cleaner, then a thorough rinse. If your cartridge has a closed end cap, let it dry before reinstalling so you don't trap moisture inside the cartridge core.
Which hot tubs and spas use the PWK65?
The PWK65 is compatible with: Hot Spring Tiger River Phoenix, Hot Spring Tiger River Bengal, Hot Spring Tiger River Caspian, Hot Spring Tiger River Sumatran, Hot Spring Limelight Bolt, Hot Spring Limelight Glow. Confirm against your owner's manual or the label inside the filter compartment, since some brands changed cartridge sizing between model years.
Dimensions
Specifications
| Outer Diameter | 8.5″ |
|---|---|
| Length | 10.5″ |
| Top Type | Open (no end cap) |
| Bottom Type | Open (no end cap) |
| Filtration Area | 65 sq ft |
| Primary Brand | Pleatco |
| Part Number | PWK65 |
Fitment notes
3-inch top and bottom openings. Tiger River: Phoenix, Bengal, Caspian, Sumatran. Limelight 2008-2017: Bolt, Flair, Glow, Pulse. Hot Spring Highlife Classic 1989-1990. Caldera 76136.