Another thing about the Mag pumps... You can easily plumb them external if you want to. I've got a Mag 18 on my closed loop, and it works great.

Of course, I should have left more room behind the tank so it would be easier to get to. That's something to think about if you do plumb one external. You need plenty of room around the pump to work the valves and unions in order to remove the pump for cleaning. Next time there'll be more room and less skinned knuckles.