Yes for that kind of control it must recirculate. I too wanted a big rez but found many setups where the rez would keep buckets topped up but not recirculate and they still have to check each bucket. I have all the fittings for a six bucket setup and a controll rez and full rez but now need a water pump to suck water from each bucket back to main rez and let gravity fill them back from the controll rez. Then i can just check main rez for PPM's and PH. Till then back to work checking each unit.

A search may help find something.