Aerating wort with an air pump. What's the proper gallon rating?

Last time I heard someone tried to use an aquarium pump and a 2 micron stone it was a failure: the pump wasn't powerful enough. With a proper pump 30 min is said to be enough. However, there was Beersmith podcast where some guys from Maltose Falcon club made a split batch with a few different aeration techniques, and aquarium pump rated below pure oxygen (obviously) and below shaking the fermenter vigorously for 1 minute (surprise!). Taken that pump+stone kit costs $60 here in Aus, I personally dropped the idea at all.