i am going to run two, two foot cubes on the top rack, a four foot on the middle rack and a four foot sump (room for expansion ). i've got my whole system designed with a fully automated water change system. although i'm having a little trouble working out the return lines to the tanks. do i run two pumps, one for each rack or just plumb the lines individually to each tank off the one pump? the advantage being of the latter i can valve each line so i can cut off tanks individually from the system. however i was concerned weather the pump would suffice for pressure this way. any suggestions would be greatly appreciated.