No problem. The pvc on the back of my tank is my return outlets. I split my 1" sump return into two 3/4" outlets and my 3/4" closed loop into two 3/4" outlets. I know that it does look like a lot of pipes and I am considering reducing the closed loop to two 1/2" retuns and painting the plumbing black. The reason that I split my returns is because 800gallons per hour is a lot of flow in a 23gallon tank and I didn't want my livestock to get blown around like inside a washing machine. By splitting returns I am able to have 100% of the flow with only half of the velocity. There is less water coming out of each 3/4" exit than you would get out of a little maxijet nozle - the result is a really gentle water movement despite having tons of turnover.
Each pump will tell you what gph it is rated for. You can get an idea of losses
using this calculator:
http://www.reefcentral.com/calc/hlc2.php
- Chad