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: 7:00 am to 5:00 pm Phoenix Time
Saturday: 8:00 am to 2:00 pm
Sunday: Closed
- We do not ship on Saturday or Sunday.
- Orders totaling more than $300 will require signature confirmation upon delivery.
- We process and prepare orders for shipment within 1 business day. Please note that many other pool supply retailers require 3–5 days of handling time before shipping.
- Orders placed after 1:00 pm Phoenix Time may not be eligible for same-day shipment.
- Expedited shipping options are available at checkout.
Return Policy:
- Products that are received damaged will receive a refund in store credit.
- Most products are eligible for return within 30 days of receipt, except where noted below.
- To initiate a return, please complete an RMA form prior to sending your item back.
- Original shipping costs are non-refundable and will be deducted from the return credit.
- Items returned missing accessories or original packaging, or that are not in the same condition as received, may be subject to a restocking fee of up to 100% depending on the condition of the item upon return.
- Some returns will be charged an automatic 15% restocking fee.
- We are unable to issue refunds for items that have been damaged or rendered inoperable due to installer error.
- Please complete the return form to receive your RMA number and return shipping label.
- Chemical products are not eligible for return under any circumstances.
- The Pentair Colorsync 618031 is not eligible for return.
- Pool cleaners are not eligible for return.
- Opened seals and o-rings are not eligible for return.
- Capacitors are not eligible for return.
- Plastic popup tools are not eligible for return.
- Automation components and circuit boards are not eligible for return.
- If a light is returned due to a reported malfunction and is found to be fully operational upon testing, return shipping costs and a restocking fee will be deducted from the refund.
- Orders refused at the time of delivery will be subject to the original shipping costs being deducted from the refund.
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