The airstone likely won't hurt, but it may not be necessary. If you have one or all of the powerheads aimed to ripple the surface of the water, you should have adequate gas exchange.

 

I reconsidered, the airstone may hurt. If you have air trapped under the live rock, this will kill anything (sponge, tunicate, etc) in this area. Also, are you running a protein skimmer? If you are, this is all the oxygenation you'll need. If you're not - it would really be a good idea.

 

 

 

It doesn't work that way. Bubbles offer an air to water interface where organic particles collect. The bubble that pops on the surface of the aquarium water releases most of these organic particles back to the water. Some will be thrown up to collect on surfaces of the light, etc. but not in any quantity which would be considered significant. Effective skimming depends on a large quantity of fine bubbles (greater surface area) to pop (outside the tank) in the throat and collection cup where the skimmate can be removed.

 

Nitrate, the molecule, occurs as a product of bacterial action. As far as I know, it does not stick to the air water interface. You may have heard that skimmers reduce nitrates. Their action of removing organic waste before it is fully broken down by bacteria is why you may have heard that a skimmer reduces nitrates. If you look at it that way, the skimmer also removes potential Ammonia and Nitrite as well as potential Nitrate.

 

Does this seem clear? Do you understand the principle?

 

For me, an air bubbler is always useful. The degree of usefulness depends on how fast the pumps are moving the water. In my 2 gallon Nano, the only circulation is the air bubbles coming from an airstone. I never worry about pH in that tank. And I don't see any ill effect with tiny bubbles getting trapped in the rock. Inverts can deal with small bubbles by pushing them away.