Move fish to a clean tank after 7 days. This reduces reinfection by tomites left behind after the initial treatments. Please don't be put off if some of this information seems too basic, or if some of this information seems unnecessary or superfluous. The only problem with 90 degree's is potential sterility of fish in the aquarium. And yes, I understand that some fish can, and will, withstand high temperatures because they have evolved techniques to deal with that issue in the wild.
Prevention is to have healthy, stress free fish, non-major temperature swings which causes stress.
I must disagree with this point.