Just a reminder that tank temps will probably go up this weekend with the anticipated hot weather... I think at one time or another we have all lost fish/corals because of this. Get those fans ready!
I found that properly fit Cellular Shades go quite a ways in keeping entire house cooler in summer... and warmer in winter. Home Depot has double cell by Bali, but if you can find and don't mind spending a little more, then I would go with Hunter Douglas triple honeycomb for best energy efficiency and sound deadening.
Also helps tremendously if you can open up the place when it is cool during the night then close everything up tight during the days.
It might make sense and cost little to set thermostat on an airconditioner to 75 on very hot days and just cool the room instead of trying to just keep a tank cool. More comfortable for us humans too.
We ended up putting a 10,000 BTU in the living room - kept it 79ish degrees in the room with the tank climbing (biocube 14) a litle bit. Everything looks good. That means we should be okay when the weather hits into the 90-95 range.
Just got it yesterday too - just in time. I'm sure if the main room was 84ish - the tank would be overheating.