the outlet and inlet on my mag7 are both 1/2", that is why i went with 3/4" for both... I read over the instructions front and back and even looked at the box and it says nothing about the diameter pipe/tubing to run, just that it has those size inlet and outlet (1/2").
Then you'll need to run 1" piping off the output of the mag.
From: http://www.melevsreef.com/closedloop.html
What sized plumbing should I use?
The Mag pump comes with printed instructions that state to double the outlet size to determine the plumbing needed. The Mag 7 has a 1/2" outlet, and the pvc needs to be 1". If you use 1" plumbing, you'll get better flow than if you used smaller I.D. (inside diameter) pvc.