Are you keeping corals? If yes, then you definently should not have glass because the glass will restrict the amount of light that will come into your tank. Also you do want to have some evaporation for gass exchange.
I have to top off my tank everyday do to evaporation. I do not have an auto top off, and I would suggest for you to look into one.
Cheers and happy reefing. It's an addiction.
