NO airstones?

Usually due to the overall surface movement and water movement of various pumps and powerheads, as well as a the potential (and recommended) presence of a protein skimmer. A lit refugium thick with macroalgae can also negate the need for airstones.

Also salt creep will get way out of control if you use a airstone...

I use an airstone in my refugium. I put it there to help combat a low pH problem and it worked. I have a fairly sealed stand and CO2 builds up in it so my short term solution was to put an airstone in the refugium with the air pump outside the stand in order to add O2 back into the tank. Once I can get a hole saw and drill a hole in the back of the stand and install a fan then the airstone will be taken out. Otherwise, ya, what everyone else said.. microbubbles in the tank being the biggest complaint, and definately salt creep is another on open top aquariums. (were the air bubbles pop at the surface of the tank and spray microscopic mist on the rim/sides of tank, once it dries out, salt is left behind and forms sheets).