The Waterway Cartridge Crystal Water [131 sq ft OEM] [Qty 4 Required] is an OEM Waterway Crystal Water cartridge element used in compatible cartridge filter systems. This 131 square foot filter cartridge helps capture debris and support cleaner water flow through the filtration system.This listing notes that four cartridges are required for the applicable filter setup, making it important to confirm the full filter model and quantity needed before ordering. Replacing worn or clogged cartridges helps maintain circulation, filtration efficiency, and overall water clarity. OEM Waterway Crystal Water replacement cartridge 131 square foot cartridge element for compatible systems Four cartridges are typically required for the matching filter Helps support cleaner water and proper system flow Part number 817-0131 helps confirm the correct replacement