Temputaure Issue HELP

I have a 75gal tank with 2 heater, 3 power heads and a T5 light 4 bulbs.



I have the heaters set at 76deg just to try and pull the temp down. Its at 84 and wont budge.... I don't understand this crazy mess at all???????



Might I add I am in the middle of a tank cycle...didn't know if it matters