Unicel spa filter cartridge C-4625 — 25 sq ft replacement for Rainbow/Waterway, 13-5/16in open-end, 106 pleats

Unicel C-4625 is a 25-square-foot replacement filter cartridge designed to match OEM specs for Rainbow, Waterway Plastics, and other compatible spa and pool systems.

This replacement cartridge gives you an easy way to restore filtration performance without replacing the whole system. Built with 4-ounce Reemay media and 106 pleats, the C-4625 balances surface area and flow to capture debris while extending time between cleanings. It fits a range of legacy brands and models, so you can bring clarity back to spa water quickly and affordably.

Will this fit my Rainbow or Waterway Plastics housing?

Unicel engineered the C-4625 to match the common dimensions and end-cap opening of many Rainbow and Waterway Plastics filter housings. Confirming your current cartridge length and diameter is the quickest way to verify compatibility.

• Overall length: 13 5/16 inches
• Diameter: 4 15/16 inches
• Top and bottom end caps: open with 2-1/8-inch inner diameters
• Compatible with Rainbow plastics 17-2325 and several legacy spa brands

How does the C-4625 improve water clarity and maintenance intervals?

The cartridge's 106 pleats increase usable surface area (25 sq. ft.) to trap particles more effectively than lower-area filters. The Reemay 2040 media is a lightweight, fine-fiber polyester that resists tearing and lets you rinse debris away, reducing how often a full cleaning or replacement is needed.

• Filter media: 4-ounce Reemay 2040 for consistent particle capture
• Pleat count: 106 for higher dirt-holding capacity
• Spec-built to meet OEM performance and flow characteristics

What are the physical details and installation points to check?

Before installing, inspect the end-cap openings and overall dimensions to ensure a snug, leak-free fit. The C-4625 uses open end caps with a 2-1/8-inch inner diameter top and bottom, so it slides into housings that accept that standard size.

• Length: 13 5/16 inches — measure your old cartridge end-to-end
• Diameter: 4 15/16 inches — check the cylinder width inside the housing
• Open top/bottom end caps — verify your housing uses open-end cartridges
• OEM cross-references include several spa brands and Rainbow part 17-2325

Why choose Unicel replacement cartridges over alternatives?

Unicel is a long-established filter manufacturer that produces cartridges to match original equipment dimensions and performance. Choosing a like-for-like Unicel cartridge helps maintain proper flow rates and pressure characteristics, avoiding stress on pumps and plumbing caused by undersized or incompatible filters.

• Meets OEM specifications for reliable fit and flow
• Durable Reemay media resists damage during cleaning
• Manufactured to consistent quality standards for repeatable results

Who this is for: The Unicel C-4625 is ideal for spa and pool owners, service technicians, and maintenance pros who need a direct-fit replacement for Rainbow, Waterway Plastics, Custom Molded Products, and a range of older spa brands. If your current cartridge measures roughly 13 5/16" long with a 4 15/16" diameter and uses open end caps, this cartridge offers an OEM-spec, high-surface-area solution to restore filtration performance and reduce maintenance time.