08-14-2008, 03:09 PM
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I see your issue now. Let me start by saying I run an external overflow on one of my systems, and have never had issues with the siphon breaking in the U-tube. As long as the flow in the u-tube is strong enough for any bubbles that enter to be carried all the way through the tube, there is little chance you will ever have a problem. They are really a lot more reliable than they may seem. There is however, an alternative to relying solely on the siphon, and that is to have a small water pump drawing water through a port in the top of the U-tube out, and back into the inner portion of the overflow unit. You can earch Ebay to find examples of these units.
Another idea is to buy yourself a reef ready tank, or if your tank is not made of tempered glass, have it drilled and build your own reef ready setup.
Personally, i think the idea you are entertaining is a recipe for disaster. If the pump output from your return line does not match the output from the pump you install in the overflow EXACTLY, you will end up with a flood. To install identically rated pumps would not suffice as the back pressure from gravity would slow the return line reducing the total GPH. Regardless even the difference of 1 cubic centimeter per day would eventually result in an eventual flood.