Planted Tank Guru
Join Date: Sep 2006
Location: Northern California
Doesn't matter really. With a glass top, you get warmer tank temperatures, usually, and condensation on the underside of glass top which may block some light from getting through.
Do you have fish that jump?
As far as the gas exchange, etc, etc, I don't think the use of a glass top will affect it much.
Evaporation in a planted tank is quite little IME so you won't have to worry much about it.