shark medicines

This shark arrived with black spots on its skin. Initially the shark seems fine. Two days later, the its skin begin to show discoloration and more black spots appeared. Attempted to dose the shark with 50 grams of sodium nifurstyrenate (100mg per 1g) in 3000 L tank. Also tried to feed the shark...

I purchased a 8 inch coral cat shark with red spots on stomach i think it may be bacteria infection what medicines are safe for coral car shark i heard metroplex Is neo plex kanaplex safe as well What about api general cure or melafix