Do either of you have the AquaFuge II? Thats the model that I have (it has an overflow box on the output rather than baffles that the original model had), it came with a Rio 600.
For the longest time, I had a problem with the output line sucking in air and putting bubble into the tank. I recently solved the problem by reducing the flow of the Rio600 feeding the fuge.
The chaeto has been growing like crazy in mine.