B - There are 4 returns on the corner overflow (two at the top, two at the bottom). Right now, it seems efficient enough for flow, but I'll likely add a NanoStream when everything grows out.
I think what made things easier was that the cube is wider than it is taller. This really allowed me to scape it more openly. It also greatly increases gas exchange, keeping the tank well oxygenated. Could be why the tangs are so happy