There is a word I like to call a lot of people, that word is "wrong". Your tank is to hot and that causes diseases not the other way around. It is very stressful for a cold blooded creature. I don't know why your fish died, but the temp didn't help it.I've researched and read that alot of people run high Temps in their tank to keep down diseases.
Read above statement. Whatever killed your foxface, it also died from lack of oxygen because hot water carries much less oxygen than cooler water. A fish does not have a disease to die.UPDATE***- Foxface found deceased. No signs of disease or fight. what the heck