Gallonage and filter capacity monitor operates at flow rates between 0.2?2.0 GPM. Accurately tracks the number of gallons of filtered water produced and alerts you when it?s time to change your filters. Also shows real-time flow rates. Displays in gallons or liters. For use with Evolution RO1000, Tall Boy, Merlin Garden Pro or any other filter systems with 3/8 in fittings with flow rates up to 2 GPM.