Unicel C-4335 | 35 sq ft Spa Filter Cartridge

By Unicel
SKU: C-4335
$37.99

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Check out the Filter Guide to see if this filter fits your hot tub model.

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Description

TheĀ Unicel C-4335Ā deliversĀ 35 square feetĀ of filtration acrossĀ 219 pleatsĀ ofĀ ReemayĀ® polyester media, capturing debris down to an average ofĀ 20 microns. Built toĀ meet or exceed OEM specifications, it's one of the mostĀ widely compatibleĀ cartridges in the spa industry — fitting systems from Bullfrog, Caldera, Sundance, Waterway, Pentair, Rainbow, and many more.

Filtration is the quiet backbone of clean spa water. Every soak leaves behindĀ body oils, lotions, hair, and fine debris, and the cartridge is what removes all of it before it clouds the water, feeds bacteria, or coats your plumbing. When a filter is worn or clogged, the effects spread everywhere: dull water, higher chemical use, softer jets, and aĀ pump and heater strainingĀ against restricted flow.

What separates a Unicel from a bargain cartridge is the media itself.Ā ReemayĀ uses aĀ trilobalĀ fiber — three-lobed in cross-section rather than round — which delivers roughlyĀ 45% more surface areaĀ than standard rounded filter fibers. More surface means more places to capture dirt and oils, higher dirt-holding capacity, andĀ more time between cleanings. PackingĀ 219 pleatsĀ into a compact 9-1/4 inch cartridge gives it real capacity for its size, andĀ chemical-resistant end capsĀ with open 2-1/8 inch ends make installation straightforward. Made in the USA.

Pro Tip:Ā Measure the length — it's the only thing separating this from the C-4950. Both cartridges share the exact sameĀ 4-15/16 inch diameterĀ and the sameĀ open 2-1/8 inch end caps, so they look identical side by side. The difference is size: theĀ C-4335 is 9-1/4 inches longĀ (35 sq ft), while theĀ C-4950 is 13-5/16 inchesĀ (50 sq ft). A tape measure against your old cartridge settles it in seconds.

Brand

UNICELĀ®

Key Features
  • 35 sq ft of filtration — full OEM-spec filtration area across 219 pleats
  • 45% more surface area — Reemay trilobal fibers outperform standard rounded fibers
  • Captures down to 20 microns — removes particles far finer than the eye can see
  • Exceptionally broad fitment — one of the most widely used cartridge sizes in the industry
  • Open 2-1/8 in ends — simple drop-in installation, top and bottom
  • Made in the USA — built to meet or exceed OEM standards
How It Works

Water is drawn through the cartridge's pleated media as your spa circulates.Ā Pleating creates the capacity: folding the fabric into 219 pleats packsĀ 35 square feetĀ of filtering surface into a cartridge only 4-15/16 inches across and 9-1/4 inches tall. More surface means water passes throughĀ more slowly and thoroughly, capturing finer particles, and it means the filter holds far more debris before flow starts to drop off.

The fiber shape is whereĀ ReemayĀ earns its reputation. Standard filter fibers are round; Reemay's areĀ trilobal, and that three-lobed cross-section packs roughlyĀ 45% more surface areaĀ into the same amount of material. More surface per fiber means more places for dirt to be trapped, and theĀ smooth media surfaceĀ releases that dirt readily when you rinse it. Unicel builds the cartridge to the original manufacturer's exact dimensions, so it seats properly in the housing — which matters, because a loose cartridge lets waterĀ bypass the media entirely.

Pro Tip: A clean filter protects your equipment, not just your water. As the pleats load up with body oils, your pump has to work harder against the restriction, and reduced flow across the heater can trigger flow-related errors. Regular rinsing and periodic deep cleaning is the cheapest protection there is for the expensive parts of your spa.

Directions for Use

Installation

  1. Turn off power to the spa at the breaker before servicing the filter compartment.
  2. Open the filter lid and clear any debris from the compartment.
  3. Remove the old cartridge, noting its orientation.
  4. Seat the new cartridge squarely in the filter well, fully seated top and bottom so both open ends engage properly.
  5. If your spa uses more than one cartridge,Ā replace them at the same timeĀ so they wear evenly and flow stays balanced.
  6. Close the lid, restore power, and run the circulation to confirm normal flow.

Routine Cleaning

  1. Every two to four weeks:Ā remove the cartridge andĀ rinse gently with a garden hose, working between the pleats from top to bottom. A soft brush cleaning tool helps.
  2. Periodically:Ā soak or treat the cartridge with a dedicated filter cleaner to dissolve the body oils and buildup a rinse can't remove, then rinse it off.
  3. Let it dry fullyĀ before returning it to service whenever possible.

When to Replace

  • The cycle between cleanings gets noticeablyĀ shorter
  • Low water flowĀ or high differential pressure
  • The media has aĀ tear
  • TheĀ center core collapses

Cartridge life depends on routine maintenance and your spa's water chemistry.

Pro Tip: With 219 pleats in a compact body, take your time rinsing. A dense pleat count is what gives this filter its capacity for its size, but it also means the folds sit close together and debris settles deep between them. Working the hose stream slowly down each pleat, all the way around, removes far more than a quick pass over the outside — and it noticeably extends how long the cartridge lasts.

Specifications
  • Brand:Ā Unicel (Meissner Mfg. Co., Inc.)
  • Part Number:Ā C-4335
  • Series:Ā Unicel 4000 Series
  • Product Type:Ā Replacement pool and spa filter cartridge
  • Filtration Area:Ā 35 sq ft
  • Pleat Count:Ā 219
  • Filtration Rating:Ā Captures debris to an average of 20 microns
  • Media:Ā Reemay spunbonded trilobal polyester, 3 oz basis weight
  • Outer Diameter:Ā 4-15/16 in
  • Length:Ā 9-1/4 in
  • Top End Cap:Ā Open, 2-1/8 in inner diameter
  • Bottom End Cap:Ā Open, 2-1/8 in inner diameter
  • End Caps:Ā Durable plastic, chemical-resistant, exact OEM fit
  • Fits:Ā Bullfrog Spas, Caldera Spas, Sundance Spas, Sunrise Spas, Waterway Plastics, Pentair Pool Products, Rainbow Plastics (Dynamic Series IV DFM/DFML), Custom Molded Products, and more
  • Cross-References:Ā Pleatco PRB35-IN, Filbur FC-2385, Guardian 409-219, Pentair R173431, 03FIL1300, 17-2482, 25393, 303557, 817-3501
  • Not the Same As:Ā Unicel C-4950 — same diameter and end caps, but 13-5/16 in long and 50 sq ft
  • Cleaning:Ā Rinse gently with a garden hose every two to four weeks; deep clean periodically with filter cleaner. Do not pressure wash.
  • Origin:Ā Made in the USA
  • Shipping:Ā Standard ground; not classified as a hazardous material

  • Outer Diameter: 4-15/16"
  • Length: 9-1/4"
  • Top End Cap: 2-1/8" open
  • Bottom End Cap: 2-1/8" open
  • Pleat Count: 219
  • Media: 3 oz.
  • Filtration Square Footage: 35 sq. ft top load
Compatibility

The C-4335 is one of the most widely used cartridge sizes in the industry, fitting systems across many brands:

  • Spa brands:Ā Bullfrog Spas, Caldera Spas, Sundance Spas, Sunrise Spas
  • Equipment makers:Ā Waterway Plastics, Pentair Pool Products, Rainbow Plastics (including Dynamic Series IV DFM/DFML), Custom Molded Products

It's cross-referenced against a long list of numbers, includingĀ Pleatco PRB35-IN,Ā Filbur FC-2385,Ā Guardian 409-219, andĀ Pentair R173431, along withĀ 03FIL1300,Ā 17-2482,Ā 25393,Ā 303557, andĀ 817-3501.

Because this size spans so many brands, the surest way to order correctly is toĀ read the part number off your current cartridgeĀ or check it against the dimensions below — particularly theĀ 9-1/4 inch length, since a longer cartridge of the same diameter is a different part. Also confirmĀ how many filters your spa takes. For upkeep, pair it with a dedicatedĀ filter cleaner.

  • Vacanza Aventine 2010-Current
  • Highland Aventine AVH 2006-2009

This is a replacement for the Caldera Aventine 74148 Filter Cartridge

Most products purchased from our online shop within the last 30 days are eligible for return. Please review our return policy to see the list of items that cannot be returned.

Some major items that are non-returnable:

  • Gift cards
  • Electronics
  • Pumps / Motors
  • Hot Tubs
  • Closeouts
  • Fireplaces
  • Electric Fireplaces
  • Massage Chairs
  • See return policy below for full list of non-returnables.

UNICELĀ® Brand FAQs

Who makes Unicel filters?

Unicel filters are made byMeissner Mfg. Co., Inc., a family business that began as a small contract sewing operation in thelate 1950sand moved into pool filtration through the 1970s. By the end of that decade the company was producing cartridge filters for the industry'soriginal equipment manufacturers, and in1985it introduced the Unicel brand as aftermarket replacements. It's still owned and operated by the Meissner family today.

Are Unicel filters as good as the original manufacturer's filter?

Unicel builds its cartridges tomeet or exceed original equipment specifications— and that's a meaningful distinction here, because the company produced cartridges for the industry's OEMs before it ever launched its own brand. Unicel cartridges usedurable, chemical-resistant end capswith an exact fit,high-capacity media,uniform pleatsfor optimal flow, and asolid corethat resists collapsing under pressure.

Where are Unicel filters made?

Unicel filters are manufactured inCalifornia, with components sourcedexclusively in the United States. The line comprisesnearly 500 products, covering replacement cartridges, D.E. grids, filter discs, and related parts.

How do I find the right Unicel filter for my spa?

Unicel cartridges areinterchangeable with all major filter brands, and each one cross-references to a list of original equipment part numbers. The most reliable method is topull your current cartridge and read the part number printed on it, then match it to the Unicel cross-reference. If the number has worn off,measure your old cartridge— diameter, length, and the size and style of the openings at each end — and match those instead. Also confirmhow many cartridgesyour spa uses.

How long does a Unicel filter last?

Cartridge life depends on how heavily the spa is used, yourwater chemistry, and how consistently you clean the filter. Many Unicel cartridges useReemayĀ® polyester media, whosetrilobal fibersprovide considerably more surface area than standard rounded fibers — which increases dirt-holding capacity and extends the time between cleanings. With regular rinsing and periodic deep cleaning, a well-maintained cartridge commonly serves a year or more.

When should I replace my filter instead of cleaning it?

Replace the cartridge when thecycle between cleanings becomes noticeably shorter, when you seelow water flowor high differential pressure, when the media has atear, or if thecenter core collapses. Pleats that stay permanently flattened or discolored after a proper cleaning are another sign the cartridge has reached the end of its service life.

About UNICELĀ®

UnicelĀ is the nation's leading manufacturer of replacement filter cartridges for pools and spas — and the story behind it is a genuinely American one. In the late 1950s,Ā Richard T. MeissnerĀ started a small part-time contract sewing operation. Through the 1970s, Meissner Mfg. Co., Inc. moved into swimming pool filter bags, then D.E. grid element covering, and by the end of that decade the company was producingĀ cartridge filters for the industry's original equipment manufacturers.

That's the detail that matters most: Unicel wasĀ building the filters that went into new spas long before it sold a replacement. InĀ 1985, the company introduced the UNICEL brand so dealers and technicians could source elements built to O.E.M. specifications from a single place — even for equipment brands they didn't carry. Today the line spansĀ nearly 500 products, all manufactured inĀ California with components sourced exclusively in the USA.

By staying focused on one thing — filtration — Unicel has built deep expertise in a critical corner of the industry, from media development to cartridge design. Every cartridge is built withĀ chemical-resistant end capsĀ for an exact fit,Ā high-capacity filter media,Ā uniform pleatsĀ for optimal flow, and aĀ solid coreĀ that holds its shape under pressure. Meissner Mfg. Co., Inc. remainsĀ owned and operated by the Meissner family, still recognized for quality and service. American-made products, world-class service.