Has anyone tried to run a fish air tank through a filtered line and an aeration stone while your fermenting? I have seen and herd about this and was wondering about its effectiveness.
I suspect it would be very effective at increasing diacetyl formation and speeding oxidation of your beer; wouldn't recommend it. Rule of thumb: once fermentation starts keep aeration/oxygenation to a minimum.
If you mean using it as a means of aerating your wort PRIOR to fermentation, that's a different story. I could list several pros and cons, but have no personal experience so will leave that to others.
Do not aerate your beer during fermentation! A sanitary aeration technique (usually just a good shake of your fermenter will do the trick) done just as you are pitching is good, after that it is not good.