Hot Spring filter sizes by collection: Highlife, Limelight and Tiger River
Most Highlife spas in our cited listings use the 6" × 10-1/2" open cartridge C-6430 (OEM 31489 / 71825 / 71826, 30 sq ft). Many 2008–2017 Limelight and Tiger River models in those listings use the 8-1/2" × 10-1/2" open cartridge C-8465 (OEM 31114 / 71827 / 71828, 65 sq ft). 2018-and-later Limelight models in the same listings use OEM 78161 / 1642301-1, which Unicel lists as both a 50 sq ft and a 75 sq ft 6" × 14" cartridge[5][38][39][24].
One product this answer points to
6" × 10-1/2" open-end Highlife cartridge.
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Three bodies, not one “Hot Spring filter”
Hot Spring is built by Watkins, and the brand has reused a small set of cartridge sizes across many collections. That reuse is why a model name alone is a weak way to order. The end cap number is the strong way. The three bodies below are the ones the Unicel 2026 guide, the Pleatco 2023 catalog, the Filbur catalog and the Leisure Time Inc. listings agree enough to publish. Where they do not agree, the paragraph says so.
| Collection, from the cited listing | OEM numbers | Unicel | Size and ends | Area on our row |
|---|---|---|---|---|
| Highlife models named for 71825, many from 1990 onward | 31489; 71825; 71826 | C-6430 | 6" × 10-1/2", open 1-15/16" both ends | 30 sq ft |
| Limelight 2008–2017 and Tiger River models named for 71827 | 31114; 71827; 71828 | C-8465 | 8-1/2" × 10-1/2", open 3" both ends | 65 sq ft |
| Limelight 2018–2026 models named for 78161 | 1642301-1; 78161 | C-6350 and C-6355 | 6" × 14", open 1-15/16" both ends. Unicel notes the original OD is 6-3/8" | 50 sq ft (C-6350) and 75 sq ft (C-6355) |
Pleatco’s cross-reference lists C-6430 as PWK30-4 and C-8465 as PWK65[2]. Filbur lists FC-3915 and FC-3960 for those same OEM numbers[31]. The 2018 Limelight cartridge is the one the catalogs do not line up, and it has its own section below. Model-by-model years are on the Hot Spring filter by model and year page and on each cartridge page.
The 6" Highlife cartridge, and the Tri-X warning
C-6430 is an open-end cartridge: no handle threads onto the housing. Unicel dates the Hot Spring use of this size to models after 1990 and prints the media as 4 oz[5]. The Leisure Time listing for OEM 71825 says many of these hot tubs take three cartridges at once, and that some models use a Tri-X ceramic filter of the same footprint instead of a pleated cartridge. The same listing says to use the pleated cartridge only where the spa specifies 71825 or a listed equivalent, and that a model which requires Tri-X needs the Tri-X filter[38].
That is a practical check, not a slogan. If you open the well and find a ceramic block rather than pleated fabric, C-6430 is the wrong object even if the footprint matches. If you find three pleated cartridges, order three. Hot Spring’s own maintenance page tells owners to replace with genuine Watkins filters[7]. An aftermarket cross-reference matches size and fittings; it is not a Watkins part. Warranty language is in your owner’s manual, not in a catalog table.
Hot Spot and some Solana models are assigned this same 6" × 10-1/2" cartridge by the dealer listings we cite, which is why those brands point back at the Hot Spring tables. Start at Hot Spot or Solana if that is the badge on the cabinet, then confirm the end-cap number.
The 8-1/2" cartridge for earlier Limelight and Tiger River
C-8465 is larger in diameter (8-1/2") and shorter than the 2018 Limelight cartridge. Both ends are open 3". Unicel, Pleatco and Filbur agree on OEM 31114 / 71827 / 71828, Pleatco PWK65 and Filbur FC-3960, at 65 sq ft[5][2][31]. The Leisure Time listing for 71827 is the source of the model years on that page: Limelight Bolt 2012–2017, Flair, Glow and Pulse 2008–2017, and a long Tiger River list that includes Bengal, Caspian, Sumatran and others going back to the early 1990s[39].
Do not put this cartridge in a 2018-or-later Limelight that calls for 78161. The diameter is 8-1/2", not 6", and the length is 10-1/2", not 14". The open-end vs threaded guide shows why the hole size matters even when you have already matched the brand.
2018 and newer Limelight: one OEM number, three area ratings
Unicel’s Hot Spring cross-reference ties both C-6350 (50 sq ft, 142 pleats) and C-6355 (75 sq ft, 229 pleats) to OEM 1642301-1 / 78161. Both replacements are printed 6" × 14" with 1-15/16" open ends, and Unicel notes that the original cartridge is 6-3/8" OD while the replacements are 6"[5]. A Leisure Time product page for 78161 gives 50 sq ft, 14" long, and about 6-1/4" OD with open 2" ends[24]. Pleatco’s 2023 catalog lists the same OEM number as PWK35B at 6-3/8" × 14" and 35 sq ft[2]. Those are three different area ratings, 75, 50 and 35 sq ft, for what the sources treat as one factory part.
We do not pick a winner. Our C-6350 page leaves the Pleatco equivalent off because PWK35B’s printed size and area do not match Unicel’s 6" / 50 sq ft row. The C-6355 page shows PWK35B and repeats the disagreement. For a 2018-or-later Limelight Beam, Flair, Flash or Pulse, order by 78161 or 1642301-1 and compare OD, length and the open ends with the old cartridge. The dealer listing we cite names those five Limelight models for 2018–2026[24].
The arithmetic Unicel publishes for area is pleats × 2 × pleat height × usable length ÷ 144[5]. That is why two cartridges with the same outside size can carry different ratings. It is also why a rating, by itself, is the wrong thing to shop for. The worked examples live in why same-size filters have different square-foot ratings.
Other Hot Spring numbers that are easy to mix in
Not every Hot Spring row is one of the three bodies above. 4CH-35 is OEM 31382 (formerly 31116): 4-5/8" × 16", molded cone handle, 1-1/2" male MPT, 35 sq ft, Pleatco PTL35-4, Filbur FC-0161. No model-year list is in the sources for that row, so we do not invent one. C-6330 shares the 6" × 10-1/2" open body and the 30 sq ft rating with C-6430 but is listed under OEM 31489 as its own Unicel number; read that page before assuming the two Unicel numbers are identical in every column. C-6600 is a different body again: 6-3/8" × 11-7/8", open 3" both ends.
If the number on your cap is not in this article, search it. The cross-reference is the index. This article is the map of the three sizes people confuse.
Care, once the size is right
Hot Spring’s filter article says a standard polyester cartridge is typically replaced every 2–3 years, and a TRI-X cartridge every 4–6 years[8]. The owner maintenance page says every three years[7]. Those are different sentences from the same brand, so treat them as a range and replace sooner if the media is torn or flow does not come back after a clean. The 2025 Highlife manual is the one that allows a dishwasher for Tri-X and not for a standard cartridge, and the 2026 Limelight manual does not mention Tri-X. Those steps are in Hot Spring Tri-X filter care. The Hot Spot collection manual says to turn power off before removing filters, not to run the spa with the cartridge removed, and not to overtighten the retainer[9]. Cleaning steps are in how to clean a hot tub filter. A clogged cartridge is also the first thing Hot Spring names when a spa shows a no-flow fault; see what a clogged or missing filter does.
Search Hot Spring part numbers on Amazon
Part-number searches
These search Amazon for the part number. They are not a check that the listing is the Watkins OEM part. Read the title and compare it with the cartridge page.
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OEM 71825 / C-6430 6" × 10-1/2" open-end Highlife cartridge.
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OEM 71827 / C-8465 8-1/2" × 10-1/2" open-end cartridge.
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OEM 78161 2018-and-later Limelight cartridge. Confirm length and diameter on the listing.
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Unicel C-6355 Unicel’s 75 sq ft replacement tied to OEM 1642301-1.
Questions
Which Hot Spring filter is OEM 71825?
71825 is one of the OEM numbers Unicel prints for C-6430, along with 31489 and 71826: 6" × 10-1/2", open 1-15/16" both ends, 30 sq ft. The Leisure Time listing for 71825 says to use that pleated cartridge only where the spa specifies it, because some models take a Tri-X filter of the same footprint.
Which filter fits a 2018 or newer Limelight?
The cited dealer listing names OEM 78161 (also 1642301-1) for Limelight Beam, Flair, Flash and Pulse from 2018 through 2026. Unicel offers C-6350 at 50 sq ft and C-6355 at 75 sq ft for that number, both 6" × 14". Pleatco lists PWK35B at 35 sq ft and 6-3/8" OD. Order by the OEM number and compare the cartridge you take out.
Can I use the 8-1/2" 71827 filter in a Highlife that takes 71825?
No. 71827 is the 8-1/2" × 10-1/2" C-8465 body. 71825 is the 6" × 10-1/2" C-6430 body. Diameter, length and the open-end size are all different.
How many cartridges does a Highlife hold?
The Leisure Time listing for 71825 says many of these models take three cartridges. Count the cartridges in the well before you order. Do not assume every Hot Spring holds three; the 2018 Limelight listing is a different part.
Sources
- Pleatco 2023 Catalog (Pentair)
- Unicel: Maintenance & FAQ
- Unicel 2026 Replacement Guide
- Hot Spring Spas: Maintenance Tips
- Hot Spring Spas: How Do Hot Tub Filters Work?
- Hot Spring Hot Spot Collection Owner’s Manual (2026)
- Leisure Time Inc.: Hot Spring Limelight 78161 filter cartridge (specifications)
- Filbur Catalog & Reference Guide
- Leisure Time Inc.: Hot Spring Highlife 71825 filter cartridge
- Leisure Time Inc.: Hot Spring 71827 filter cartridge
This guide summarizes published manufacturer and public-health guidance; always follow your own spa’s owner’s manual. See our disclaimer.