82 is not too hot and 78 is not to cold the ocean can swing more than that in one day, granted you want to keep it as constant as you can, a little temp swing isn't bad. My tank right now stays about 80 - 82, durring the summer it is 81 - 84. If you want it to stay in the upper range add a heater. If you want to cool it down you can look into removing or replacing anything that makes heat. For example if you have a sump or fuge and the pump is submerged you can use an external pump to cool it down a little. I don't have a heater on my tank and I only have a 2 in fan built into the lights. I agree that a larger fan in your tank will evaporate the water at a faster rate. Also I agree with the suguestion that you can raise or lower your lights to adjust the temp some. You just have to play with the equipment untill you find what works for you.