uhhh.. how did that happen.. I recomended 500gph when you first brought this up.. and I said if you got advice from most anyone else they would strear you to too much flow..
you could use the mag 18 for the closed loop.. but that seems like alot you wont louse any gph
to head preasure in a closed loop.. it should still work though..
I would just look in the classified sections of forums for a smaller pump..