Return Pump Question

[Ron99]

I picked up a Mag 9.5 to use as a return pump for the 65 gallon tank. My question is this: Is it best to run the foam intake attachment on it or do most of you run them with the intake open?

I am thinking the foam will just be a nitrate factory unless I wash it every few days and it may also block any critters from the refugium part of the sump from making their way into the tank.