The Zoomed 501, as from what I have heard from many users, is that it is not strong enough to pump 'up' from under the tank, and does best sitting next to/behind the tank at the same level so the motor doesnt burn out and the impeller stops. I would think of instead spending the money over and over again on getting Zoo501's, is to make the investment into a Eheim or Xp1 and just have it sit under your desk. You can still go to Lowes or whatever and get clear tubing for it too.
"You think you have tomorrow, but when tomorrow comes it's not tomorrow; it's now- and that's all you have" - Marc Johnson
Ehei-Pimpfen 276 yo!