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.
