If you want to flood your tank w/ bubbles for better gas exchange, don't bother. The best thing that you can do for gas exchange is to agitate the surface of the water. Get an Aquaclear 402 powerhead and angle it towards the surface.
Even better, if you really want to maximize gas exchange, get a small magdrive pump (like a 2) and put it on the bottom of your tank, output facing upwards toward the surface. It will pull the water from the bottom of your tank and blow it up to the top while agitating the surface. Don't try this w/ a sand substrate.