iSpring F7-CTO 1-Year Replacement Filter Kit for 5-Stage Reverse Osmosis, 7-Pack 1-year supply of replacement filters for 5-Stage RO systems Includes 7 filters Fits 10" standard filter housings, compatible to most RO systems, includes Watts Premier, Flowmatic, PuROLine, Crystal Quest, Apec, and etc. Individually wrapped, fresh from factory Use CTO in both 2nd and 3rd stages