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.