Most of the oxygen that is introduced into the tank occours at the surface of the water. A powerhead placed low in the tank will push the water around the tank such that all the water will eventually make it to the top. I'd recommend a maxi-jet 900.
Ok thanks.
Don't the powerheads make tons of tiny bubbles? I havw 2 Aquaclear 301 powerheads from the last time I had my tank set up and they made lots of bubbles..
Linda