Need advise oh keeping my nano reef temp cool.

I'm in day 7 on my cycle for my 10 gallon reef tank and I notice that my tank has been at 80-82 during the day and at night it stays at 80. I've turned down the heater and it's still hot. Where I live we get very hot summers and after summer is over it's pretty much cold after that what should I do. It's not a big deal now since I don't have anything I'm the tank that could die but I'm just planning ahead of time. Since later I will add fish and coral also I have no light on it at the time.