PWK30 / C-6430 / FC-3915
30 sq ft replacement filter cartridge • 5.875″ OD × 10.5″ long
Hot Spring has used this 30-square-foot cartridge across a huge span of its lineup. It fits Highlife tubs like the Grandee, Sovereign, Prodigy, Jetsetter, Vanguard, and Envoy going back to 1991, along with the Hot Spot Relay, Rhythm, and Tempo and the Solana line. If your Watkins-built tub takes a single filter with 1-15/16-inch openings on each end, this is it. Watkins sells it as 31489; Unicel calls it C-6430 and Filbur FC-3915. Before you buy, check whether your tub runs one cartridge or a pair, since Hot Spring configurations vary. Pop the filter lid and count. If there are two, replace both at once so they load evenly.
Compare on Amazon
PWK30 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 | PWK30 | Primary |
| Unicel | C-6430 | Equivalent |
| Filbur | FC-3915 | Equivalent |
| OEM | Watkins 31489 | Original Equipment |
| OEM | Hot Spring 31489 | Original Equipment |
Always verify dimensions and end-cap type before purchasing a replacement.
Compatible Hot Tubs & Spas
The PWK30 (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 | Jetsetter |
| Hot Spring | Prodigy |
| Hot Spring | Sovereign |
| Hot Spring | Grandee |
| Hot Spring | Vanguard |
| Hot Spring | Envoy |
| Hot Spring | Hot Spot Tempo |
| Hot Spring | Hot Spot Relay |
| Hot Spring | Hot Spot Rhythm |
| Hot Spring | Solana |
Frequently Asked Questions
What are the dimensions of the PWK30?
The PWK30 is 5.875 inches in outer diameter, 10.5 inches long, with an open top and an open bottom. Total filtration area is 30 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 PWK30?
PWK30 is the same physical cartridge as C-6430, FC-3915, plus OEM versions like Watkins 31489, Hot Spring 31489. Same dimensions (5.875" × 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 31489 the same filter as the PWK30?
Yes. Watkins 31489 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 31489 (along with Hot Spring 31489) and PWK30, C-6430, FC-3915 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 PWK30?
Mid-size spa cartridges like the PWK30 (30 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 PWK30?
The PWK30 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 PWK30?
The PWK30 is compatible with: Hot Spring Jetsetter, Hot Spring Prodigy, Hot Spring Sovereign, Hot Spring Grandee, Hot Spring Vanguard, Hot Spring Envoy, Hot Spring Hot Spot Tempo, Hot Spring Hot Spot Relay, Hot Spring Hot Spot Rhythm, Hot Spring Solana. 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 | 5.875″ |
|---|---|
| Length | 10.5″ |
| Top Type | Open (no end cap) |
| Bottom Type | Open (no end cap) |
| Filtration Area | 30 sq ft |
| Primary Brand | Pleatco |
| Part Number | PWK30 |
Fitment notes
1-15/16 inch top and bottom openings. Hot Spring Highlife, Prodigy, Sovereign, Grandee, Jetsetter, Vanguard, Envoy 1991-present. Hot Spot Relay, Rhythm, Tempo. Solana.