I have a 75 gallon and have been experiencing the same problem over the past few weeks with the water temp being to high. What I do is I take 5 gallon buckets, fill the first with saltwater (ensure correct specific gravity etc..) and leave the 2nd empty. In the night when it's cool outside I leave the 5 gallon bucket that's filled with water on the terrace so that it get cool. When the morning comes I take the empty bucket and fill it with 5 gallons from the 75 gallon tank and replace the missing water with the 5 gallons that was cooling teh night before. Repeat the process the following night, only take the 5 gallons that you drained from teh tank and put it on the terrace/outside to cool. also, what you can do is leave the covers on the tank open, it'll help somewhat. You can add the 5 gallons of cool water gradually until the temp drop to normal, it has been working for me the past few weeks.