I agree that open tops are much better. However, I think it is difficult to avoid a temperature differential between the water surface and the air because of the heat that the lights generate.If there is apossibility for you to keep the environmental temperature and tank temperature same or at most 1-2 degrees evaporation will be minimum and with an open top you will have a much better viewing pleasure IMO.
With Tek Light "legs", there would be air separation between the glass and the lights which would keep the glass from getting too hot. Other companies also make light stands.gibmaker said:I used to use tank covers on my 125 gal until I upgraded to 4 CF's. They would actually crack my glass tops from the heat! I went through about 4 free replacements and then gave up.