The quality you expect with the performance you need, so you can enjoy your pool worry free. Total filtration area: 340 Sqft. 3 Top and bottom Inside diameter (open hole). Nominal dimensions : 20″ L x 7″ OD x 3ID. End caps are both open with polyurethane material to provide high impact and perfect seal, our core is injection mold creating more stability than drilled PVC pipe. Waterway Crystal Water 325. Crystal Water 325 sqft. Cartridge meets OEM specifications. This Package contains 4 Cartridges.