I have a separate res for the Auto Feed tent and another for the Ebb & Flow, RDWC is 7 thirteen gallon totes, 6 can be used as grow sites and the 7th is outside the room, they call it the control bucket. It's amazing how quickly nutrients dumped in the control bucket make it to the back of the system. My well water is about 50-75 ppm and 2 minutes after I dump the dry nutes in the control bucket the PPM of the return water is at the target. I do have a top off res but I dont use it until later in the grow