The bottom connection fitting determines whether a replacement cartridge actually works, and a difference of just a fraction of an inch can ruin an entire weekend. Mistaking a coarse male pipe thread for a fine SAE thread or an open hole leads to unfiltered bypass water and persistent low-flow heater errors on your control panel. When water slips around the edges instead of pushing through the pleats, grit circulates straight back into the tub, pump impellers strain under uneven pressure, and an evening soak turns into frustrating mechanical troubleshooting. Flimsy pleats can also buckle under pump suction within weeks, leaving you with cloudy water and brittle end caps degraded by heat.
A proper cartridge drops into the canister smoothly, locks tight, and restores crisp water clarity with full jet pressure. Getting that effortless fit comes down to verifying three core points: outer diameter, core length, and the exact threading style molded into the base. Pairing those measurements with chlorine-resistant end caps and dense Dacron pleats traps fine sediment reliably while making weekly hose rinses quick and painless. Here is how the leading options compare for direct canister fit and dependable water care this 2026.
【NSF/ANSI 50 Certified】 Poolpure Pool and Spa filter is tested and certified by IAPMO against NSF/ANSI 50. Poolpure filter delivers safe and clear purified water to inspire the highest sense of happiness. Enjoy your unique SPA time.【Replacement Models】 Length: 10 1/2”; Outside Diameter: 5 7/8”; Top
Key specs
- Fitting Dimensions
- Length: 10 1/2 inches
- Outside diameter: 5 7/8 inches
- Top and bottom openings: 1 15/16 inches open
- Filtration Media
- Trilobal fabric provides 30 square feet of surface area to trap sediment, hair, and grit while releasing trapped solids under a standard hose rinse.
Pros:
- Certified by IAPMO against NSF/ANSI 50 standards for material safety
- Trilobal fabric structure captures fine debris and rinses clean during regular maintenance
- Direct replacement for Watkins 31489, Unicel C-6430, and Filbur FC-3915 systems
- Three-pack configuration allows rotating clean filters while dirty ones soak
Cons:
- Open 1 15/16-inch holes on both ends make it incompatible with threaded filter housings
- Outer diameter of 5 7/8 inches will not fit narrow 5-inch spa canisters
✅ Filters May Be Green or Blue ✅ REPLACEMENT FILTER - Get purer, cleaner water in your pool or spa with these replacement cartridge filters compatible for Unicel C-4325, C-4326, Filbur FC-2390, and Pleatco PRB50-IN and PRB68. See below for alternative filter names. Filters May Be Green or Blue✅ DIME
Key specs
- Canister Fit
- Designed with matching 2 1/8-inch open holes on top and bottom, this 13 5/16-inch cartridge slides over internal standpipes in compatible skimmers.
- Pleat Material
- USA-made spunbond trilobal media
Pros:
- Uses USA-made spunbond trilobal media engineered for straightforward debris release during rinsing
- Slim 5-inch diameter fits tightly into standard PRB25-IN skimmer wells and canisters
- Two-pack bundle enables quick cartridge swaps so filtration stays active during cleanings
- Matches common Unicel C-4326, Filbur FC-2375, and Pleatco PRB25-IN specifications
Cons:
- Dual open 2 1/8-inch ports will not thread into MPT or SAE threaded bases
- Compact 25 square foot rating offers less pleat area than 50 square foot versions of identical size
【NSF/ANSI 50 Certified】 Poolpure Pool and Spa filter is tested and certified by IAPMO against NSF/ANSI 50. Poolpure filter delivers safe and clear purified water to inspire the highest sense of happiness. Enjoy your unique SPA time.【Replacement Models】Length: 13 5/16”; Outside Diameter: 5”; Top Hole
Key specs
- Filtration Media
- Constructed with trilobal fibers designed to capture fine dust, sand, and hair, releasing buildup cleanly when sprayed every two weeks.
- Canister Compatibility
- Directly replaces Pleatco PRB25-IN and Unicel C-4326
- Fits Filbur FC-2375, FC-2370, and Waterway 817-2500
- Requires 5-inch diameter canister with 2 1/8-inch standpipe
Pros:
- Certified by IAPMO against NSF/ANSI 50 for water contact safety
- Trilobal dirt-locking fabric releases trapped particles smoothly during bi-weekly rinses
- Direct drop-in fit for Pleatco PRB25-IN, Unicel C-4326, and Filbur FC-2375 housings
- Comes in a two-pack to avoid spa downtime while one cartridge is soaking
Cons:
- Requires a 2 1/8-inch standpipe slip fit and cannot thread into screw-in housings
- Warranty coverage is limited to 90 days from purchase
【NSF/ANSI 50 CERTIFIED】 TOREAD Pool and Spa filter is tested and certified by IAPMO against NSF/ANSI 50. The filter with certified safe materials provides you with clean, fresh and clear water. Only select certified filters for your family to ensure the safety, health and happiness of your loved one
Key specs
- Fitting Dimensions
- Length: 10 1/2 inches
- Outside diameter: 5 7/8 inches
- Top and bottom openings: 1 15/16 inches open
- End Cap Construction
- Built with chlorine-resistant, break-resistant end caps and a reinforced central core to resist collapsing under hot tub pump pressure.
Pros:
- Certified by IAPMO against NSF/ANSI 50 for material safety standards
- Features 25 percent thicker trilobal fabric for enhanced dirt-holding capacity
- Reinforced center support and chlorine-resistant end caps prevent structural deformation
- Matches Watkins 31489 and Pleatco PWK30 dimensions across Hot Spring spa canisters
Cons:
- Open 1 15/16-inch ends cannot mount onto threaded skimmer fittings
- Wide 5 7/8-inch body will not enter standard 5-inch diameter filter wells
KEEP POOL OR SPA FRESH: The S1 Cartridge Filter is sure to keep your PureSpa Jet Massage water clean and freshMULTI PACK: 6-pack of Intex Type S1 filter cartridgesULTIMATE FILTRATION: Made with easy to clean, heavy duty Dacron paper for the ultimate filtrationCAN BE CLEANED AND REUSED: For maximum e
Key specs
- Spa Compatibility
- Designed specifically for Intex PureSpa models including 28403E, 28407E, 28443E, 28453E, 28421E, 28423E, and 28413E.
- Maintenance Schedule
- Rinse weekly and replace monthly or sooner
Pros:
- Genuine fit engineered specifically for Intex PureSpa inflatable hot tub filter housings
- Dacron paper pleats trap fine dirt and body oils in low-pressure inflatable spa pumps
- Generous six-pack supply provides multiple complete replacement cycles
- Quick drop-in installation requires no tools or threaded adapters
Cons:
- Designed solely for Intex PureSpa models and will not fit Coleman or SaluSpa pumps
- Dacron pleats require weekly rinsing and monthly replacement under typical use
Compatible Model: Type VI Spa and Hot Tub Filter Replacement Cartridge compatible with Coleman SaluSpa filter, Lay-Z-Spa, Intex and other inflatable hot tub filter - Fits all Spa Models Requiring Type VI Filters.Perfect Fit: Our type VI SPA filters measure 4.1” x 3.1”. You will get 12 premium type V
Key specs
- Spa Compatibility
- Fits inflatable hot tub pump housings requiring Type VI filters, including Coleman SaluSpa 90352E, 58323, 90427E, and Lay-Z-Spa units.
- Pack Quantity
- 12 individual Type VI cartridges
Pros:
- Bulk twelve-pack provides extensive replacement supply for high-frequency spa rotations
- Compact 4.1-inch by 3.1-inch profile drops directly into standard Type VI pump housings
- Broad compatibility covers Coleman SaluSpa, Lay-Z-Spa, and Bestway inflatable models
- Backed by an extensive two-year warranty and thirty-day return policy
Cons:
- Sized exclusively for compact inflatable spas and cannot be used in rigid acrylic hot tubs
- Small filter surface area clogs rapidly if not checked and rinsed every few days
【PERFECT FITMENT】Summer PooL & Spa Filter compatible with Unicel 6CH-940, PWW50P3(Not PWW50P4), Filbur FC-0359, Waterway Plastics 817-0050, 25252, 378902, 03FIL1400, HTF0245RT. Replace the pool cartridges for Intex above ground pool pump. PlEASE CHECK YOUR MODELS BEFORE PURCHASE!【DIMENSION & COMPATI
Key specs
- Connection Type
- Equipped with a molded circular top handle and a bottom 1.5-inch coarse SAE thread that secures directly into compatible front-access skimmer plates.
- Canister Compatibility
- Replaces Unicel 6CH-940 and Filbur FC-0359
- Matches Waterway 817-0050 front access skimmers
- Replaces PWW50P3 but does not fit PWW50P4
Pros:
- Features a 1.5-inch coarse SAE screw-in bottom thread for secure front-access skimmer mounting
- Provides 45 square feet of trilobal fabric to trap sand, silt, and hair effectively
- Integrated top circular handle allows effortless removal from deep spa skimmer canisters
- Direct replacement for Unicel 6CH-940, Filbur FC-0359, and Waterway 817-0050 assemblies
Cons:
- Uses coarse SAE threads and will not screw into fine MPT threaded fittings
- Incompatible with PWW50P4 configurations despite matching the PWW50P3 profile
REPLACEMENT MODELS: Compatible with 303279, FC-2402, Free Flow Hot Tub Filter.SPECIFICATIONS: Length: 9 1/2”; Outside Diameter: 5 3/8"; Top: Closed with String Handle; Bottom: 1 1/2" MPT Thread.EASY TO CLEAN: This filter utilizes fabric structure design so as to make the impurities easy to be releas
Key specs
- Connection Type
- Designed with a closed string-handle top and a 1 1/2-inch MPT fine male threaded bottom that screws into specialized Free Flow, AquaTerra, and Fantasy spas.
- Thread Specification
- 1 1/2-inch MPT fine thread (replaces FC-2402)
Pros:
- Features a 1 1/2-inch male MPT fine thread for threaded Free Flow and Fantasy spa canisters
- Top string handle allows easy extraction from narrow upright filter wells
- Solid end caps provide rigid support against hot water degradation and pump suction
- Direct replacement fit for part numbers 303279 and Filbur FC-2402
Cons:
- Fine MPT thread does not fit coarse SAE threaded receivers
- Sold as a single filter cartridge rather than a multi-pack bundle
Contains 2 filter cartridgesDimensions(inch): 13 5/8"x 4-15/16"; (handle and 2" Female SAE Thread)Compatible models:PWW50L, Unicel 4CH-949, Filbur FC-0172, SD-01143, 817-4050, PDC570-AFS, Rising Dragon 50.Baleen AK-90091, Magnum O250, Darlly 42522, Excel Filters XLS-479.(Part number of manufacturer
Key specs
- Bottom Fitting
- 2-inch female SAE threaded base
- Surface Area
- Dense intersecting fabric woven with 180 individual pleats provides 50 square feet of total filtration media to maintain strong flow and capture debris.
Pros:
- Features a 2-inch female SAE threaded bottom connection to screw directly onto male fittings
- Dense 180-pleat fabric layout delivers 50 square feet of effective filtration area
- Integrated top handle simplifies unscrewing and lifting the cartridge from deep wells
- Direct drop-in match for PWW50L, Unicel 4CH-949, Filbur FC-0172, and Waterway 817-4050
Cons:
- Female 2-inch SAE base does not fit 1.5-inch threads or slip-fit standpipes
- At 13 5/8 inches long, it requires significant canister depth to seal properly
Provides clean and clear water by introducing our Type VI filter cartridgeD.I.M: 4.1 x 3.1", for all spa models using Type VI filters, compatible with Bestway, Lay-Z-Spa, Coleman and SaluSpaPremium quality dacron fabric collects hair, leaves, dust, sediment, sand, etc; easy to clean and replaceFor b
Key specs
- Cartridge Size
- 4.1 inches diameter by 3.1 inches height
- Maintenance Schedule
- Clean pleats frequently with fresh water and replace the cartridge every few weeks under heavy spa use to protect low-power inflatable pump motors.
Pros:
- Exact 4.1-inch by 3.1-inch dimensions match standard Type VI inflatable hot tub housings
- Dense Dacron fabric captures fine silt, hair, and grit without choking pump water flow
- Six-pack bundle offers multiple spare filters for regular bi-weekly rotation
- Fits popular inflatable spa lines including Bestway, Lay-Z-Spa, and Coleman SaluSpa
Cons:
- Incompatible with rigid hot tubs or spas requiring Type S1 or threaded cartridges
- Requires frequent cleaning and replacement every few weeks during periods of heavy use
✅ Filters May Be Green or Blue ✅ REPLACEMENT FILTER - Get purer, cleaner water in your pool or spa with these replacement cartridge filters compatible for Pleatco: PTL18P4-4, Unicel: 4CH-21, Filbur: FC-0121. See alternate filter names below. Filters May Be Green or Blue✅ DIMENSIONS - Diameter: 4 5/8
Key specs
- Pleat Material
- USA-made spunbond trilobal media
- Port Configuration
- Top: Molded semi-circular pull handle
- Bottom: 1 1/2-inch male MPT fine thread
- Directly fits Dream Maker and Gatsby spa housings
Pros:
- Features a 1 1/2-inch male MPT thread for a secure twist-in seal on compatible spas
- Spunbond trilobal media facilitates easy washing and reliable particle retention
- Rigid molded top handle makes cartridge extraction and re-threading straightforward
- Direct replacement for Pleatco PTL18P4-4, Unicel 4CH-21, and Filbur FC-0121 in Dream Maker spas
Cons:
- Male 1 1/2-inch MPT thread does not fit coarse SAE receivers or open standpipe skimmers
- Compact 8-inch length and 4 5/8-inch diameter offer limited capacity for larger hot tubs
Last update on 2026-10-08 / Affiliate links / Images, Product Titles, and Product Highlights from Amazon Product Advertising API
How do you measure an old hot tub filter to ensure a replacement cartridge fits?
Measure three specific areas: the outside diameter across the plastic end cap, the overall length from end to end, and the center hole diameter. For open-hole cartridges, measure across the inner circle, which typically spans 2 1/8 inches open or 1 15/16 inches on both top and bottom openings. If your cartridge has molded handles or bottom threads, measure the pleated body length separately from the fittings. Check the stamped part number on your original end cap, such as Unicel C-4326 or Watkins 31489, to confirm matching specifications before ordering.
What is the difference between open hole, MPT threaded, and SAE threaded filter connections?
The difference lies entirely in how the bottom opening seals inside the filter canister. Open-hole cartridges have smooth 2 1/8-inch openings on both ends that slide straight down over an internal standpipe. An MPT fitting has male, fine-pitch threads, such as a 1 1/2-inch MPT thread, that screw into a dedicated port at the canister base. In contrast, an SAE fitting uses coarse threading, found on cartridges with a 1.5-inch SAE thread or a 2-inch female SAE thread. Mixing up coarse SAE threads and finer MPT threads prevents the filter from seating, which allows bypass water to circulate uncleaned.
Which replacement filters fit portable inflatable spas compared to rigid acrylic hot tubs?
Inflatable spas use compact cartridges with smaller surface areas, while rigid hot tubs require taller, high-capacity filtration media. Portable models like Coleman SaluSpa, Lay-Z-Spa, and Intex rely on compact Type VI cartridges measuring 4.1 inches by 3.1 inches, or Type S1 cartridges for PureSpa systems. Rigid spas take much larger cartridges, such as 25 square feet units measuring 5 inches by 13 5/16 inches, 30 square feet models measuring 10 1/2 inches long, or 45 square feet filters measuring 6 inches by 8.3 inches. While small filters trap floating silt in portable spas, heavier grit settling on the floor often requires a dedicated hot tub vacuum cleaner to keep water clear.
Why does a hot tub pump display flow error codes after installing a new cartridge?
Flow errors occur when water cannot pass freely through the cartridge into the circulation pump, usually caused by an improper bottom fitting or trapped air. Forcing an incompatible thread type into the intake port restricts water passage and trips internal pressure switches. Air trapped inside the dry pleats during installation can also create an air lock in the plumbing lines. Verify that the cartridge diameter and length match your spa model, seat the bottom connection completely, and bleed excess air from the canister before restarting the filtration cycle. Shielding the water with an insulated hot tub spa cover also prevents heavy outdoor debris from prematurely choking filter pleats.
What safety and water standards apply to replacement hot tub filters?
Check for cartridges certified by IAPMO against NSF/ANSI 50. This certification confirms the filtration materials maintain structural integrity and deliver purified water without leaching chemical compounds under heated spa conditions. Manufacturers of compatible replacements for Unicel C-6430, Pleatco PWK30, and Unicel C-4326 maintain NSF/ANSI 50 certification to confirm performance in hot water. Always confirm certification markings directly on the product label or packaging documentation.
How long do hot tub filter cartridges last before needing replacement?
Rigid spa filter cartridges typically provide up to a 12 months service life under regular maintenance, while smaller inflatable cartridges require much earlier replacement. Rinsing pleats with water whenever jet pressure drops or water turns cloudy helps maintain proper flow rates. Replace any cartridge immediately if the end caps crack, the pleat material tears, or regular rinsing no longer clears flow restrictions.
