Just an fyi, some fish don't tolerate the mid-80's very well. My female responds very badly to water warmer than 78 degrees, and lower than 74. She gets very pale and lethargic with cold water (this was before I knew better and hadn't given her a heater) and extremely lethargic with stress lines with warmer water (this was after I got the heater set to 76 and then told I should gradually warm it to 80 for optimum health). And during a water change, she does better if colder water is put in her tank, rather than warmer water.
Just a thought if he takes a turn for the worse again.