IMO, 83 is not too bad, as long as that is the top end
however lighing and motors will affect it, as well as natural occurances within the eco system. If you have a heater, try runnign it without it
also, teh fan may help some
lastly, does it recieve any sunlight at all?? or any other type of light whcih may increase the temp? If it is in sunlight, I would move it for this reason as well as other maintenance reasons