Pleatco PTL18P4 = Unicel 4CH-21 = Filbur FC-0121

18 sq ft hot tub filter, 4-5/8" diameter × 8" long. Top: Handle · Bottom: 1-1/2" MPT. Pleatco application: Pageant Spa Top Load.

Interchangeable cartridges

Unicel 4CH-21 confirmed by: Pleatco p.47 (Unicel to Pleatco cross reference) Unicel p.7 (Cartridges by series (dimensional listing))
Filbur FC-0121 confirmed by: Pleatco p.48 (Filbur to Pleatco cross reference) Filbur p.33 (Reverse cross reference (Unicel to Filbur))

Unicel 4CH-21 rates it 19 sq ft (vs 18 sq ft); filter area ratings differ by maker.

Each manufacturer measures a little differently. Compare these with your old cartridge.

Search any retailer for 4CH-21 or PTL18P4 or FC-0121. These are the same cartridge under different brand names.

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As printed in the cited aftermarket catalogs. Match the number on your old cartridge or in your spa manual exactly.

OEM number	Listed in
`20245-238`	Pleatco p.31: OEM part # column Unicel p.55: OEM cross reference: Saratoga Spas
`PVT-25N`	Pleatco p.31: OEM part # column
`PVT 25N`	Unicel p.63: OEM cross reference: Vita Spas

From the spa-manufacturer cross reference in the Unicel 2026 Replacement Guide. A brand may use several sizes, so check your measurements.

What is the Unicel equivalent of Pleatco PTL18P4?

The catalogs cross-reference Pleatco PTL18P4 to Unicel 4CH-21.

What is the Filbur equivalent of Pleatco PTL18P4?

The catalogs list Filbur FC-0121.

What size is the PTL18P4 filter?

Pleatco lists PTL18P4 as 4-5/8" outside diameter by 8" long, top: Handle, bottom: 1-1/2" MPT, 18 sq ft.

Which OEM part numbers does it replace?

Listed OEM numbers: 20245-238, PVT-25N, PVT 25N.