raise it slowly over the next couple days to 84-86. Are the red spots bumps, or sores? Salt does work, if you feel his life is in danger add 1 tbsp of evaporated sea salt per 5 gals of water. Also daily water changes. RTC are tough, but I have found that when they get sick they will deteriorate very fast unless you conduct tons of water changes. Also what size tank is he in. He might be producing more waste than your filtration can handle and thus causing ammonia burns on his body. Also check for uneaten food as it can foul the water and make him sick. Hope some of this helps.