Ebb & Flow (aka Flood & Drain) is a recirculating system where nutrient is pumped into the top tray, thereby flooding the root system until it reaches the overflow, where it ebbs back into the resevoir. These are the deluxe range and come with pump and fittings, an adjustable overflow, emergency overflow, 125ml of phosphoric acid, pH test kit, a segmental timer and a TMU timer.