I don't know what more airstones would get you, quite frankly - as long as you've got some good bubbles going, that's really all you need - you've probably got MORE airstones than you need ... but it IS a big bucket!
I AM concerned about what you said concerning the water level in your bucket - that it was right at the bottom of the netpot and this isn't good. You need to leave a space of at least 1/2 - 1" between the bottom of the netpot and the water... the roots need that humidity zone and will die without it...
Good luck!