very cool bud. Wish I would have seen this earlier. If it's not up and running and your willing to make a change I have a good suggestion. Instead of running a return line to each tank, it would work good to run 1 return line to the top tank, then plumb the outlet of that tank into the next level below, then the bottom level to your sump. Less pipes, less backpressure to deal with, and less plumbing. The one problem you will have is the sump must be a good deal below the outlets for the bottom level. It's a good idea to use valves on each outlet so you can quiet it down. If you don't have them filled, you can drill a hole in the bottom and use a standpipe and bring it right down to the tank below. I ran a rack system similar to this awhile back and that was the best setup I could come up with. Look around FHUSA and you can find pictures.