From previous posts:
At the risk of raising the ire of people like Dr. Ron Simek, who advocates warm tanks, in the range of 83F, like on the reef, I believe that thermal stability is more important than the exact temperature for most species of marine fish and live corals:
1) I would not worry about the system temperature, if most things are growing fine
2) I would not worry about the temperature, if it does not vary by more than 5 degrees Fahrenheit (F) from the low (high?) of the day to the high (low?) of the night
3) Just what does your tank measure first thing in an early winter morning compared to the middle of a sunny summer afternoon? How much difference is there?
4) One temperature-controlled fan (about $50) might be just the ticket to get the heat out of the hood.
5) Are you venting the top of the hood, to make sure that heat can escape? Good ventilation can be worth as much as 2-3 degrees F in cooling.
6) Are there A/C vents in your home that you can direct over the tank? If you can close 15-25% of your least used vents and open the one over the tank, you can cool your tank another few degrees without lowering your household temperature.
7) Where is your highest household temperature set? If you set your heater (only one watt per gallon required in Florida) for just one degree F over the room temperature, the heater will provide much needed thermal stability to the tank.