You need as much evaporation as you can get unless you live in Alaska with the windows open....
Evaporation is a cooling process. It dissipates the heat coming from all these pumps and lights. If you don't allow it you'll boil your fish.
My tank, a 52g reef, evaporates a gallon a day, and I'm happy about that.
The equipment you need is an autotopoff, a float-valve in your sump with an electrical switch that turns on a small pump in a bucket [there are other designs] to deliver a tiny spurt of fresh ro/di water to your sump. This means any evaporation is made up by tablespoons, not by cupfuls, so there's no salinity spike, and no disturbance of your corals, or accidental bath in fresh water.
Look at
www.autotopoff.com for a cheap and basic topoff system and lose the lid, not only on your display, but also on your sump. Your temperature will be a pain to stabilize until you do.
In summer, you'll want to blow fans across the water down there to further speed evaporation.
The other thing mentioned, gas exchange, is where your live sand emits pure nitrogen gas bubbles toward the surface: this is the final product of the breakdown of biowaste in your tank, and it needs to escape.
