i keep mine no higher then 77 and no lower then 75. i read that the hoter the watter the faster the fishes matabolism. thus the more they poo and more poo the more ammonia and thats a no no. but thats just me...
There is no differnce between temps of 77 and 83 or thereabouts. Keeping it constant or as close to constant is all that matters.
Mine is at 81 right now, but goes as high as 82 and as low as80. No difference in the tank whatsoever.