This was exactly my concern, Dman. With a reef tank, you need an open top. Lots of air exchange helps everything.
But reef tanks do not typically have airstones bubbling in them as we all do for our growout tanks, and typically they don't use wet/dry trickly filtration. These two things in combination may be enough air exposure to take care of atmospheric balancing of CO2 and other gasses.
I am at a bit of a disadvantage compared to some of you in that I presently do not run a protein skimmer, yet another way to get air into your water.
So far so good, though. The fish seem not to mind, water condenses on the glass instead of the rest of the house, and I've left an opening in all the tanks for water to enter, airline to enter and siphon tube to do its work.
Autofeeding is a bit more of a challenge, as the air that emerges from the openings is very humid and condenses on the feeders, rendering them useless. I am trying pumping dry air into the feeders so that it will exit where the moisture is coming in. This worked in 3 of 4 feeders last night, and we will see how it goes.
Cheers,
Kathy