I'm building something like you are asking about with PVC and a QuietOne pump. I'll probably have to get another pump however, I'm not sure I trust this pump not to leak. I'm putting a ball valve on the return to simulate more head to the pump and slow downthe return flow. The CO2 injection will be on the inlet to the pump though, get the bubbles of CO2 to fight gravity as well as the flow.
Aquascape? I'm a crypt farmer.
It's a fine line between fishing and standing on the shore looking like an idiot.
That IS an aquascape, it's titled "The Vacant Lot".