This sounds very interesting, thanks for sharing this. Id personally get an activated carbon filter for the exhaust. If you can make one, that would save you a bit of money. If you think that the water is not very oxygenated, i say its best to over oxygenate a little than being less oxygenated. Id like to read of the progress with your system. when i grew outdoor plants they absolutely loved and flourished from my aquarium water. There was a huge difference when i starting watering them this way. Be careful of the fish pecking at the roots as they may cause further damage. Can a fine net just above the water perhaps stop them doing this in any way? ..just a thought.. good luck!