Epsom salt 1 tablespoon for every 5 gallons. It is mainly to help with tissue swelling and letting it go back inside on its own. It's strange yours is listed at 99%, it should be 100%. What are the ingredients on the package?
What are your water parameters? Ammonia, nitrite, nitrate? I have a feeling your tank isn't truly cycled which will be awful.
Chill out on all the medicines and treatments, decrease the heat slowly and do a series of water changes before adding the epsom salt. Flowerhorns are already genetically weak to begin with, bombarding them with a million medications and stress factors such as high heat, ammonia, nitrite, etc is going to make the situation far worse.
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