• Fits: Spas that use the Pleatco PTL18-4, Unicel 4CH-21 or Filbur FC-0121 cartridge
• Size: 4-5/8" × 8" · 19 sq ft
• Brand: Neptune, part # 44NC650121
• Not sure? See all compatible part numbers
• Ships from Canada · priced in CAD · no customs or duty

About this filter

The Neptune 44NC650121 replaces the Pleatco PTL18-4 cartridge used in hot tubs and spas. It's built to the same dimensions and filtration area as the Pleatco PTL18-4, so it drops straight into your filter housing with no tools. It's a clean, cost-effective alternative to the brand-name cartridge.

Is this a Pleatco filter? No. This is a Neptune compatible replacement made to the same size and fit. Pleatco, Unicel and Filbur part numbers are listed only so you can confirm compatibility.

Filter substitution notice: If the Neptune cartridge is unavailable, we may ship a compatible equivalent with the same dimensions, end caps and filtration area.

Specifications

Compatible part numbers

If your old filter shows any of these numbers, this cartridge replaces it:

• Neptune 44NC650121
• Pleatco PTL18-4
• Unicel 4CH-21
• Filbur FC-0121

How to measure your old filter

Stand it on end and check two things: 4-5/8" wide and 8" tall. If both match, it fits.

Why buy from AquaMagic Depot

• 🇨🇦 Canadian stock: Priced in CAD and shipped from Canada. No border fees at delivery.
• 🔧 Real parts people: Send us a photo of your old filter and we'll confirm the fit before you order.
• 📦 The right fit, guaranteed: We reserve the right to ship a compatible equivalent of the same size and performance when needed.

Questions

Is this a Pleatco filter?
No. It's a Neptune compatible replacement built to the same size and fit as the Pleatco PTL18-4.

How many do I need?
Replace the same number of cartridges your filter currently holds. If it holds more than one, replace them all together for even flow.

How often should I replace it?
Most owners replace pleated cartridges every 12–18 months, or sooner with heavy use, torn or flattened pleats, or if it won't come clean.

How do I clean it?
Hose it down between the pleats every few weeks, and soak it in filter cleaner once or twice a season. Let it dry fully before reinstalling.

Can I return it?
Unused filters in original packaging can be returned under our return policy. Filters can't be returned once installed, so confirm the fit first. We're happy to check it for you.

Pleatco, Unicel and Filbur are trademarks of their respective owners and are used only to show compatibility.