You're really pushing the limit of your 30 filter. If you under filter your tank, then you must do large, weekly water changes. 60 to 70 percent of the tank's volume, with your current filtration would really be in order.
I have large tanks and use filters smaller than recommended, but I'm a water change fanatic and that's the only reason I can use them. If you're willing to follow this WC
routine religiously, then in my opinion, it can be done.
I don't believe airstones provide much oxygen help under normal circumstances, but in your tank any added surface movement would be helpful.