Most reefers feel stressed because they believe the animals we keep need a rock solid temperature to make it. Nothing could be further from the truth, and it actually sets them up for disaster should something go wrong. It was by accident that my tank hit 87 one day...I had left the halides on "manual on" by accident with no AC, or normally they would have shut off at 84( THE upper limit according to common belief). The tank never looked happier. After that, I have had my tank approach 88, and that is when I kill the halides. But even then, I truly see zero signs of stress from my animals. However if they went to that temp from a tank that is kept at a rcok solid 80 with a combo of chiller and heater, most would perish.
I could run the tank cooler if I wanted, but I dont even kick the fans on until it hits 83-84 on my tanks. The swings that high are only in the hottest of summer. The peak this year has been 86 tank temp. This is also with a velcoity 110 watt pump, known for adding heat. I could ditch that and the pemp would easily fall 2-4 degrees. Not all my heat is halides, though it is obvious from temp graphs when they come on.