Skimmer?
Powerheads?
Canister Filter?
How much water turn over you have?
I've never seen air stone's directly in the main display a salt water reef before, but it doesn't mean it can't be done. Personally I don't like to see the bubbles anywhere in the main display, and I take measures to make sure they don't end up there when being returned from my sump and refrigum. With enough water turnover and good skimming air stones shouldn't be needed.
No airstones in the tank except for rare occations such as power outages or very low PH. The bubbles interfere with the lighting somewhat and can be irritating to fish and corals.
They are great in sumps as long as the bubbles stay there.