I have read that air stones do not put alot of O2 into a tank because the bubbles do not diffuse and once they hit the surface it escapes (similar to Co2 I assume). Many people say a hang off the back filter like an AC will do just as good if not better than an air stone. Still others suggest that it is water movement that provides the best O2. So I guess my question is, what does work best for getting extra O2 into the water? I ask because people have told me to add extra O2 to the water when my CO2 is not running. Seems like a good idea but I'm not sure the best way to accomplish this. It is a 180 planted tank with pressurized CO2 and several barbs, angels, tetras, lve bearers etc. Oh, and it has a Fluval FX5 with the outflow 2 inches under the surface in the middle of the tank. One output facing each end. Thanks in advance for your input!