AFFORDABLE REPLACEMENT: Replacement 31489 spa filter for 30 sq ft Hot Spring Spas and Watkins Spas and any systems that needs 5 7/8 inch (diameter) by 10 1/2 inch (length) filters INCREDIBLY SIMPLE TO USE: Easily replace your old 31489 filter, Filbur FC-3915, Unicel C-6430, Pleatco PWK30 spa filter with the Tier1 spa filter 31489 EXTREMELY DURABLE: Durable & Washable 30 sq ft Pleated Fabric Filter Media to capture sediment and other contaminants with its high strength, high flow design to give you industry leading flow rates for 3 month before your next filter change SPA FILTER CARTRIDGE REPLACEMENT: This Tier1 Watkins 31489 replacement filter can be used in place of your PWK30 spa filter. 100% TIER1 NO WORRIES GUARANTEE: We stand behind the quality of filtration and overall performance of our Tier1 filters!