Are you just wanting to do this to increase your input into the SCWD?
I would recommend keeping your return line from the sump simple. If you want to incorporate the SCWD, build yourself a simple closed loop. You can place the pump (mag 7) higher up of the ground and reduce your head pressure, and this will allow easier maintenance to your entire system.
You'll need to have a pipe hanging into your tank that will siphon water out of the tank, into the pump and then back into the tank via the SCWD. check out www.melevsreef.com
to find out instructions on doing this.