Like everyone already said 86 degree's and salt at 1 tablespoon per 5 gallons.
I would get some MelaFix, too.
If that spot on it's fin is in fact a secondary bacterial infection you'll know it within a matter of 48 hours - the increased temperatures will make it grow fast.
Keep us posted - if you start to see any kind of cottony or fuzzy growths get some PimaFix in there.