Check the listing for details. Spa Filter - 4CH-21 Replacement Spa Filter 20 sq/ft. Condition: New. Listed at 25.67 USD. Guardian Spa Filter - 4CH-21 - Replacement Filter 20 sq/ ft 4CH-21 Replacement Filter 20 sq ft Guardian Pool Filter Replaces Unicel 4CH-21, Pleatco PTL18P4-4, Filbur FC-0121 Filter Cartridge for Swimming Pool and Spa Keep your water sparkling clean with top of the line pool/hot tub filters. This cloth filter traps micro particles ensuring sparkling clean water. 4CH-21 In-line Cartridge - Used by many manufactures from Alcove, Altera, DM Industies, Dream Maker Spas, Maax Spas of AZ, Pagent Spas, Saratoga Spas, Vita Spas and many more! With Advanced Free Flow Core for better cleaning Will work with other manufactures filters including: 20245-238, SD-00845, SD-00821, SD-00838, 17-175-1025, PTL18P, PTL 18, PVT-25N, PA17, PA13 Features Outside Diameter: 4 5/8"Length: 8"Media Weight - 3 oz.SQ FT Media - 20Unicel - 4CH-21 Filbur - FC-0121 FC0121Pleatco - PTL18P4-4 NOTE: Filters should be replaced once every 6 months to ensure max flow through rate.This unit is brand new and is for the 20 sq ft filter cartridge. Filter housing canister is sold separately We accept PayPal and Credit card (Visa or Mastercard). If you are ordering multiple units and part, please call us to see if we can save you shipping cost for multiple item orders. No taxes to US residence! Please allow 4-6 days for shipping via UPS Ground to USA or Canada. You will be emailed a tracking number to the email address you provide us. Expedited Shipping services are available!Your #1 Hot Tub Parts Replacement Store!