I may not be seeing everything here, but the issue I see is the return water from the refugium to the tank. The height of the refugium tank is irrelevant, only the water height matters. In that diagram, there is not enough water height to get the water pressure alone to move water from the refugium overflow to the main tank. I don't see a problem with the rest of it. It looks like an overflow setup, so you can't go by the water level in the tank, only by the water level inside the over flow. You would need the overflow level to be higher than the water level in the main tank. I would think much higher to effectively work in the fashion you are looking for. I'm guessing the overflow height would need to be at the same level as the highest part of your return line into the other tank, since it's not a siphon.
I don't know if I've adequately described what I see as the problem. Basically if you take it just like you have it drawn, but raise the entire setup on the right to raise that water level to the highest point of the return tube farthest to the left I think would work the way you envision it.
I think that raising the water level higher in the refugium will give you the movement from the refugium back to the main tank, but at that point I do think you might have some trouble with the head pressure on the canister moving the water back the other direction.
Last edited by Bandit1200; 06-24-2014 at 09:44 PM.