New pump

Using the return as a major player in your circulation volume is a difficult thing. I would use the 3 circulation pumps and whatever came from the sump would be a bonus. It is recommended to run the return pump at head at 10 times the sump's volume.

 

You could just have a third section of the drain, with 3/4s of the flow, that lets right out into the return section of the sump. Then, have multiple outlets for the pump in the back of the tank (for good flow patterning), one of which is above the bottom of the overflow teeth to break siphon.

 

That is the setup I am running right now. With two circulation pumps now.

 

I am currently running a quiet one 4000 1017 gph and it is pretty good and quiet