Dirty water after a busy weekend can turn your hot tub into the least inviting place in the house. The correct cartridge depends on the tub’s model, connection type, and available filtration area, so measuring before ordering saves you from a frustrating fit. These six options cover common fixed and inflatable hot tubs for 2026, with distinct strengths for drop-in, threaded, and screw-in systems.
A Closer Look At The Lineup
POOLPURE PRB25SF Spa Filter
Beckacher RELX-TIME Spa Filter
Cryspool 28 Sq.Ft PDM28 Spa Filter
Cryspool 2402 Watkins 303279 Spa Filter
Cryspool 04072 C-4326 Hot Tub Filter
INTEX Type S1 PureSpa Filter 6-Pack
The Strengths Of Each Pick
Water that picks up hair, leaves, and grit after several busy evenings calls for enough filtration media to handle the load. The POOLPURE PRB25SF Spa Filter provides 50 square feet of filtration area and a 50-micron layer, giving you a substantial working surface without moving to an oversized cartridge.
Its three-lobed fiber structure increases the exposed surface between the pleats, which are the folded sections that trap debris. Compared with screw-in filters made for inflatable tubs, this fixed-size cartridge suits permanent drop-in installations and several common replacement numbers.
A Few Strong Suits
- The 50-square-foot area suits tubs that collect debris during frequent use.
- Reinforced end caps and an integrated core help the cartridge hold its shape.
- The 50-micron media targets fine particles that ordinary filter paper may miss.
- Its dirt-locking fabric is designed to release captured grit more easily during rinsing.
- Compatibility spans PRB25SF, C-4405, FC-2387, R172464, and several other listed models.
Practical Considerations
- Confirm the 6 5/8-inch length, 5-inch diameter, and 2 1/8-inch openings before ordering.
Key Specs
Who It Suits Best
You benefit most from this cartridge when your spa uses one of its listed drop-in models and needs generous filtration area for steady, heavy use.
A Better Fit Elsewhere
The Cryspool 2402 Watkins 303279 Spa Filter suits a specialized threaded housing that cannot accept the POOLPURE cartridge’s open ends.
An inflatable spa can collect lint, dust, and sunscreen residue quickly, especially with several people using it each week. The Beckacher RELX-TIME Spa Filter uses screw-in construction and trilobal fabric to fit the water inlet, making it aimed at RELX, Aleko, Wejoy, Aquaspa, and CO-Z inflatable tubs.
The four-filter bundle gives you a practical rotation for periods of heavy use. Cleaning is straightforward: remove the cartridge from the inlet, scrub the pleated surface, and rinse away loosened particles before putting it back.
A Strong Showing
- Four cartridges reduce the inconvenience of cleaning and reinstalling one item.
- Four protective covers help keep stored replacements separate from dust.
- The dense pleats provide more surface area than standard filter paper of the same size.
- The screw-in format suits compatible inflatable spa water inlets.
Trade Offs
- The listed replacement interval can be as short as every two or three days during heavy use.
- Six pieces require enough storage space to keep the covers and cartridges organized.
- Compatibility is concentrated on named inflatable-tub brands rather than universal fit.
Made For
You get the most value from this set when you own a compatible inflatable hot tub and prefer maintaining several clean cartridges at once.
Another Choice May Suit
The POOLPURE PRB25SF Spa Filter is a better fit for a fixed drop-in spa with open ends and substantially more filtration area.
Smaller drop-in housings need a cartridge that fits without forcing the end caps into place. The Cryspool 28 Sq.Ft PDM28 Spa Filter measures 7 1/4 inches long with 3-inch openings at the top and bottom, giving you a more compact profile than several longer replacements.
Trilobal fibers create a deeper, three-dimensional filtration structure than basic point-bond fabric. For a PDM28 system, regular rinsing helps trapped debris leave the pleats, while the reinforced pleats and caps keep the cartridge steady inside the housing.
What Earns Its Place
- The compact dimensions suit systems designed around the PDM28 profile.
- Twenty-eight square feet of area provides a middle ground between smaller and larger cartridges.
- The deeper trilobal structure supports effective collection and easier rinsing.
Points To Note
- Compatibility centers on PDM28 and 461273 models without oval ends.
- The 28-square-foot area offers less capacity than the 50-square-foot POOLPURE option.
Feature Snapshot
Right Fit For
You benefit from this cartridge when your hot tub accepts a PDM28-style replacement and a compact 28-square-foot filter meets your filtration needs.
Consider Something Else When
The Cryspool 2402 Watkins 303279 Spa Filter makes more sense for a Watkins unit requiring a threaded bottom and closed top.
Threaded hot tub housings call for a cartridge whose lower connection matches the plumbing rather than a standard drop-in cartridge. The Cryspool 2402 Watkins 303279 Spa Filter has a 1 1/2-inch MPT threaded bottom, while a closed top and string handle simplify handling during removal and installation.
At 9 1/2 inches long, this filter has a more specialized profile than the Cryspool 28 Sq.Ft PDM28 Spa Filter. That distinction matters because the closed top and threaded base make it a direct fit for the Watkins, FC-2402, and related models listed for this cartridge.
Real Benefits
- The MPT thread provides a direct connection for compatible housings.
- The string handle gives you a convenient way to lift the cartridge.
- Trilobal fibers support deeper impurity collection within the pleats.
- Reinforced caps and pleats help the cartridge remain stable during installation.
Details To Watch
- Confirm the 1 1/2-inch MPT thread and closed-top design before ordering.
Technical Sheet
Who Will Love This
This cartridge suits you when your Watkins, Free Flow, or Lifesmart hot tub uses the specified threaded and closed-top configuration.
Where A Sibling Pick Shines
The POOLPURE PRB25SF Spa Filter is the better option for a drop-in housing with 2 1/8-inch openings rather than a threaded base.
Some drop-in hot tubs use a long cartridge that reaches farther into the housing than a compact model. The Cryspool 04072 C-4326 Hot Tub Filter measures 13 5/16 inches long and provides 25 square feet of filtration area, offering a middle-sized option for the systems it fits.
Both ends have 2 1/8-inch openings, so the cartridge is designed for a drop-in arrangement rather than a threaded connection. Its compatibility list includes C-4326, FC-2375, PRB25-IN, 303909, and several additional replacement numbers, giving you useful flexibility across related hot tubs.
Positive Takeaways
- The 25-square-foot area offers useful capacity without the longest housing profile.
- Open ends make it suitable for drop-in filter wells.
- A broad compatibility list covers several similar replacement models.
Possible Compromises
- The 13 5/16-inch length requires adequate clearance inside the housing.
- The 25-square-foot area is smaller than the 50-square-foot POOLPURE option.
- Both opening sizes must match before the cartridge can seat correctly.
Built With In Mind
This filter suits you when your hot tub uses a C-4326-style long drop-in cartridge and you need a balanced 25-square-foot replacement.
Swap It Out When
The POOLPURE PRB25SF Spa Filter fits more compact drop-in housings and provides twice the listed filtration area.
Inflatable PureSpa users often need a replacement cartridge sooner than a fixed hot tub because skin oils, body lotion, and loose fibers enter the water during frequent bathing sessions. The INTEX Type S1 PureSpa Filter 6-Pack keeps six matching cartridges together for an easy rotation.
Having a spare available makes your maintenance routine less rushed. You can remove the dirty cartridge, rinse it according to the hot tub’s care guidance, and let another dry before the next cleaning, assuming your PureSpa specifically uses the Type S1 cartridge.
What Makes Sense
- Six cartridges support regular changes and convenient cleaning rotations.
- The pack reduces the need to reorder replacement cartridges one at a time.
Factors To Consider
- Confirm that your PureSpa requires the Type S1 cartridge before ordering.
- Keep six cartridges dry and organized so bent pleats do not affect installation.
Quick Facts
The Right Fit
You benefit from this pack when your inflatable PureSpa uses a Type S1 filter and you regularly entertain or use the tub throughout the season.
Reach For A Different Pick When
The Beckacher RELX-TIME Spa Filter is a better fit for a compatible RELX-family inflatable tub rather than an INTEX PureSpa.
Match The Cartridge To Your Spa
Start With The Connection Type
A drop-in cartridge rests inside a housing, while a threaded model screws into the base and a screw-in cartridge enters through an inflatable tub’s water inlet. Measure the opening and check the manufacturer’s replacement numbers before ordering, since similar-looking cartridges can have very different connections.
Compare Dimensions And Filtration Area
Length determines whether the cartridge clears the housing, while diameter and end openings determine how it seats. Filtration area also matters: larger areas can handle more debris before cleaning, but they do not compensate for a poor physical fit.
Match Capacity To Your Use
A lightly used spa may handle a smaller cartridge, while frequent gatherings create more hair, dust, and lotion in the water. The POOLPURE PRB25SF Spa Filter and INTEX Type S1 PureSpa Filter 6-Pack suit different needs, with the former offering greater area and the latter supplying several cartridges for regular changes.
Inspect The Existing Cartridge
The old cartridge gives you the clearest starting point for size, connection, and shape. Check the end caps, threads, handle, and overall length, then compare those details with the replacement listing rather than relying on the hot tub brand alone.
Common Fit Problems And Better Upgrades
Mistakes Worth Dodging
Buying by hot tub brand alone can lead to the wrong connection, and ignoring dimensions may leave the cartridge unable to seat properly. Check the exact replacement numbers and compare both openings, especially when a cartridge resembles a listed model but has a different bottom connection.
What Separates Premium From Basic
A larger filtration area, reinforced end caps, and a structured fiber medium can improve the cartridge’s practical role in a heavily used spa. The added cost matters more for frequent use, while a correctly matched smaller cartridge may suit a lightly used tub better.
Frequently Asked Questions
How Do I Know Which Hot Tub Filter I Need?
Match the cartridge to your current filter’s length, diameter, openings, and connection type. The manufacturer’s replacement numbers provide a second check for your spa model.
Can I Use a Pool Filter in a Hot Tub?
A pool filter may share similar dimensions, but hot tubs also use screw-in and threaded designs that differ from conventional pool cartridges. Use a cartridge specifically listed for your spa’s model and connection.
How Often Should I Replace a Hot Tub Filter?
Replace it when cleaning no longer restores adequate flow or when the manufacturer’s maintenance guidance calls for a change. Heavy use can shorten the interval, particularly in inflatable spas with frequent bathing sessions.
Are Longer Hot Tub Filters Better?
A longer filter can suit a deep drop-in housing, but length alone does not determine filtration quality. You need a proper fit, sufficient filtration area, and the correct connection for your hot tub.
Should I Keep Spare Filter Cartridges?
Keeping a spare makes maintenance easier and prevents delays when a cartridge needs frequent cleaning or replacement. Store the extras dry and flat so the pleats and end caps remain in good shape.
Final Verdict
Your hot tub’s connection and housing dimensions should make the decision before brand names or filter area. A large drop-in system may suit the POOLPURE PRB25SF, threaded units call for the Cryspool 2402, and inflatable tubs need the matching screw-in or Type S1 design. Once the fit checks out, choose the capacity and maintenance schedule that suit how often the tub is used.