i don't see what the problem here is, my tank stay's between 83 and 85, and my fish and coral are thriving, i used to keep my temp between 75 and 78 until i read up on water temps for coral and fish and what i found out was that the coral's will thrive on it and the fish do not mind as long as you move the temp up slowly, since i keep mine warmer, i have seen a vast improvement in my coral they are growing at an alarming rate, to the point that i could frag every month.
Hope this helps
Melissa V.