that is way to hot. a poor mans chiller is how i control the temp when the halides are on. walmart clip on to come on when lights turn on. 77 is where it should be set, if you have coral
My heater is set at 78. With the heat from pumps and lights, the water temp is usually around 78-81. IMO, 84 is not considered too hot and clip-on fan or computer fan will take care of it. High temperature in summer months is natural for corals but not fast temperature swing. As long as your temp goes up and down slowly, it will be fine.