I keep it at 75 only because i can do so without a chiller
I always figured 78-81 was because people couldn't. That being said I know tons of people who keep there tanks as high as 84 degrees with no ill effects whatsoever. The only thing about temps i would see being any sort of an issue would be in acclimation. from a 75-76 degree tank to an 84 degree tank...but even the lfs in calgary i would wager don't do 75. I really picked 75 because it was the first temp people agreed on when i asked...a long time ago. Stuck with it ever since. You'll be fine, I take issue with any lfs or anyone for that matter telling me sometyhing like that thouigh..offering advice is one thing...but, oh well. If your livestock is happy i'd say you are doing the right thing