I used to have an open top 55G reef.
Then, people in the forum suggested to get glass tops on so that (a) no bad stuff lands in the tank's surface, (b) help keep the temps from jumping too high, (c) helps prevent too fast evaporation which causes fluctuations in SG
prior and after a top off, and (d) it prevents salt creap from going places (like fan inlet of my CUSA Orbi 4x65w fixture).
So far, my temps stay between 78F at night and 80F when the daylights plus actinics are on. It's been a couple of months since I purchased the "flippable" glass tops. The corals are doing really well. Top offs have been much less than before. And salt creap has been reduced greatly.
I have powerheads all over the place in the tank. 400GPH Aquaclear with quickfilter attachment pointing towards the surface which aids in surface agitation, 175 GPH
Aquaclear with oscilating wave maker, and 270 GPH
Aquaclear pointing towards LR
rock-work to prevent settling of detrius and keep dead spots from happening.
I think I have a good amount of water movement which increases the possibility of gas exchange.
Wouldn't glass tops be OK as long as you have ample water circulation and movement?