TOREAD 35 sq.ft Spa Filter Cartridge Replacement – Fits Unicel C-4335 / Trilobal Fabric, NSF‑50 Certified

TOREAD PRB35-IN is a 35 sq.ft replacement spa cartridge engineered to match Unicel C-4335, Guardian 409-219 and similar in-line filters while delivering improved dirt-holding and long-lasting construction.

Designed for in-line spa and hot tub systems, this TOREAD filter uses a trilobal filtration fabric and reinforced end caps to trap particles more efficiently while preserving water flow. Certified to NSF/ANSI 50 and produced to Pool & Hot Tub Alliance standards, the cartridge is a direct-fit compatible replacement for several popular part numbers. It’s built for routine cartridge swaps and offers a balance of filtration capacity, durability and easy installation without requiring backwashing.

How does this filter improve water clarity compared with the original cartridge?

The PRB35-IN uses a high-performance trilobal fabric that increases the effective filtration area and captures finer particles than many standard cartridges. That means fewer visible particles and longer intervals between cleanings while maintaining pump efficiency.

• 35 sq.ft filtration surface for greater dirt capacity
• Trilobal microfibers capture smaller debris particles
• Tested to NSF/ANSI 50 for material safety and performance
• Maintains water flow so circulation systems run normally

Will this cartridge physically fit my spa—what are the exact dimensions?

This replacement is sized to match common 35 sq.ft inline cartridges and fits systems designed for Unicel C-4335 and like models. Check the measurements against your existing element to ensure a correct match before purchase.

• Overall length: 9 1/4 inches (approx.)
• Outside diameter: 5 inches
• Top and bottom opening diameter: 2 1/8 inches
• Filtration area: 35 square feet

What materials and construction features make it durable?

The cartridge pairs thicker filtration fabric with robust end caps and a reinforced center core to resist chlorine exposure and mechanical stress. These enhancements reduce the chance of cracking and extend the usable life compared with thin, economy cartridges.

• 25% thicker filtration fabric for higher dirt retention
• Heavy-duty, chlorine-resistant end caps and center support
• Designed for in-line use—do not backwash
• Manufactured using certified, spa-safe materials

Which models and part numbers does it replace—and is it an OEM part?

The PRB35-IN is a compatible aftermarket replacement designed to work with several manufacturer part numbers. It is not an OEM product; manufacturer names are provided only for cross-reference to help you find the right fit.

• Compatible with Unicel C-4335 and Guardian 409-219
• Also fits Aladdin 13501, Rainbow Dynamic 35, Waterway 35 in-line and similar
• Sold under the independent TOREAD brand as a compatible spare part
• Meets industry filtration standards and PHTA guidelines

Who is this for: The TOREAD PRB35-IN is intended for owners of above-ground and in-ground hot tubs or spas that require a 35 sq.ft in-line cartridge and previously used Unicel C-4335/Guardian 409-219 style filters. It’s a good choice for anyone seeking a certified, longer-lasting cartridge that holds more debris between cleanings while preserving pump performance. Avoid using this cartridge in systems that require backwashing; follow your spa manufacturer’s replacement guidelines for best results.