Not a chance
Actually alot of tropical keepers keep there tank temps around 90. Like peacock bass keepers and alot of characin keepers.
Why are you worried about disease with no fish?
And if you are getting ready to stock the tank I guess it is already cycled?
If its not being cycled with ammonia and you now you have a parasite pr disease problem then run some bleach thru the system. Do a 100% water change and don't add any dechlorinator and then pour in a few cups of bleach to raise the chlorine levels more then the tap water.
Let that run for a day and then do another 100% water change and add a triple dose of dechlorinator to the fresh water.