Keeping evaporation down is a bad thing.. you WANT evaporation. Not only does it add to the cooling of the tank, but it also is vital for the oxygen transfer process of the water itself. It helps increase O2 in the water, helps maintain a higher pH and helps the tank maintain temps on those warmer/humid days.
So keep the glass tops off.. maybe add some fans. The AC will help with humidity or you can buy a de-humidifier.
