Unicel Replacement Filter Cartridge 50 sf Cal Spa/Martec | C-4305
Unicel
SKU: C-4305
Unicel C-4305 Replacement Spa Filter Cartridge – 50 Sq Ft (Open Top & Bottom, 2-1/8" ID)
The Unicel C-4305 is a premium 50 sq ft pleated replacement filter cartridge used in many hot tub and spa filtration systems that take a 4-15/16" diameter cartridge with open ends. Replacing a worn or torn cartridge helps restore circulation, improve water clarity, and reduce strain on the spa pump and heater.
Key Features
- 50 sq ft filtration area for strong debris capture and steady flow
- Open top & open bottom design for standpipe-style housings
- Durable pleated media and rigid inner core built for repeated cleanings
- Common replacement when pleats are torn, flattened, or won’t clean up well
Specifications
- Part Number: C-4305
- Filtration Area: 50 sq ft
- Outside Diameter: 4-15/16" (4.9375")
- Length: 14-7/8" (14.875")
- Top End Cap: Open
- Top Inside Diameter: 2-1/8" (2.125")
- Bottom End Cap: Open
- Bottom Inside Diameter: 2-1/8" (2.125")
- Pleat Count (typical): 193
- Media: 3 oz pleated media
Replaces / Cross References
- Filbur: FC-1630
- Pleatco: PMT45 (often also listed as PMT50 depending on application catalog)
- Darlly: 40454
- Sundance: 6540-497 (common reference)
- Other references: 15003
Compatibility Notes
- Many spas use similar-looking cartridges—confirm by matching the OD, length, and 2-1/8" open ends.
- If your current filter has a handle, threads, or a different inside opening, you likely need a different cartridge.
When to Replace
- Pleats are torn, frayed, or separating from end caps
- Filter stays restrictive even after a deep clean and thorough rinse
- Water stays cloudy despite proper sanitizer and balanced chemistry
- End caps are cracked/warped or the inner core is collapsing
Related Products
- Unicel C-4305 (Shop / Options)
- Spa Cartridge Filter Cleaner
- Cartridge Cleaning Wand
- Spa Water Test Strips
- Spa Scale Remover
Maintenance Tips
- Rinse the cartridge regularly (often weekly with heavy spa use) to prevent restriction and keep jets performing well.
- Deep clean every 3–6 weeks with a cartridge cleaner to remove oils; rinse thoroughly before reinstalling.
- If scale is present, degrease first, then treat for scale, and rinse completely before returning the filter to service.
- Rotating between two cartridges (one in use, one drying after cleaning) can extend overall filter life and improve performance.
Questions about returns? View our return policy.
Hours Of Operation:
Monday - Friday: 8:00 am to 4:00 pm Phoenix Time
Saturday and Sunday: Closed
- Orders costing more than $300 WILL be required to have signature confirmation upon delivery.
- Handling time is typically only 1 day.
- Any item ordered after 1pm Phoenix time, may not ship same-day.
- Call us if you require expedited shipping and we can give you quotes based on your needs.
Return Policy:
- All products, except as noted below, are eligible for return up to 30 days after receipt of item.
- For returns, an RMA form must be filled out HERE or customers can call for additional help.
- Shipping costs will be deducted from all returned items.
- Any item that is missing accessories, original packaging, or is not returned in the same condition that it was received in, may be subject to a re-stocking fee up to 100% based on the condition we receive it in.
- Items broken, damaged, or inoperable due to installer error will not be refunded.
- Fill out the return form or give us a call to obtain an RMA and return shipping label.
- There are no returns on the Pentair Colorsync 618031
- No returns on pool cleaners.
- No returns on opened seals and o-rings.
- No returns on capacitors.
- If a light is returned because it "doesn't work" and it tests fine, the cost to ship and a re-stocking fee will be deducted from the refund.
- All products denied upon arrival at customers house WILL be charged the cost to ship.
- Visa Gift Card Promotions: Gift cards are sent within 14 days of the order. When accepting the Visa Gift card, you agree that if your order is returned or refunded, this amount will be deducted from the refunded amount. All Visa Gift cards are sent via email in an E-Gift Card format and are non refundable.
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