We have an all-glass 75gal. with overflow, and use a rio 2500 running wide open to return the water to the tank. You will have to figure in the distance back up into the tank(head pressure), in feet. I guessed that mine was about 4 feet with the elbow fittings(I'm pretty sure elbow fittings add a foot, correct me if I'm wrong). So you will have to buy a pump larger than your overflow is rated. And I would stay away from the RIO's, this one's getting noisier every day(and it's not even six months old)and I've heard of them melting down on others. I'm currently looking for a replacement.
HTH,
B
[ May 11, 2001: Message edited by: KDLBEM ]