Just out of curiosity, does everyone keep tanks covered year round? Come winter I get so much evaporation beyond my needs I cover maybe 90% of top and same deal for sump. I have some DIY Cree LED's that I just ramp up the voltage to make up for the glass barrier. It definitely helps keep the tank warmer. Skimmer takes care of most of the air exchange.
I also have a 1" EPS (blue or pink styrofoam sheets you see at Depot and Lowes R value of 5) on back of tank and under it along with a side sheet on one panel that isn't viewable (60 cube in corner). I'm using 2 200 watt ebo jagers but one is just backup set at a lower temp and doesn't go on.
when it gets warmer I take the glass off and turn the fans on to get the better air exchange and evaporation needed.
I know this probably doesn't work for most situations but I plan eventually on doing a basement sump and will definitely be using the EPS foam on all sides and bottom (again removable for summer benefit). I'll see if I can figure out a plan for the top. Ideally if you can get the EPS directly on the surface of the glass this works best.