I just researched the gravity rez and float valves so that cleared that up. I do have one more question about your system though. The water in the control rez is kept at the exact height you want the water in the buckets at correct? So then where does the water pump get incorporated into moving all the water around? Is the pump just in the rez split four ways into the white tubing and then clamped off at the end and then split again into the buckets? Hope that made sense. Peace