Tacit Blues
Aquarium Advice FINatic
The leak was in the bubble counter lid. Since it all seems to be in happy equilibrium right now I just pulled it out of the system and plugged the source bottles directly in to the tank, and I've got a nice steady stream of bubbles. The bubble counter is now slathered with probably more caulking than was needed, but waste not etc. I'll let it cure nice and good before I put it back into the system and if it still leaks than I'll probably have to get a new lid for it.