Tier1 13.31 in. x 5 in. 50 sq. ft. Pool and Spa Filter Cartridge for PRB50-IN, FC-2390, C-4950 TIER1-PAS-1447 - The Home Depot
Amazon.com: Cosyspa Hot Tub Filter | Spa Pool Standard & Screw in Replacement Cleaner Cartridges | Compatible with All Inflatable Hot Tubs [Pack of 1/6/12] (Screw in, Pack of 6) : Patio, Lawn & Garden