Colin is about to use a huge danner 1200 pump i believe. Just look at Mag Drive, Eheim, and Danner and see what has the best flow rate at the height of your tower. Might be a good idea to have two resevoirs with one feeding a pump to only pump to the top of the tower, and then the one you have to go from the resevoir at the botttom of the tower through the comp, to the other resevoir.