all good thing to add to the food I use garlic extreme and selcon or garlic and zoecon. Are the fins tattered any if so I would lean to-wards a fungus and would also treat tank with melifix. It helps in the healing process, the black areas maybe where the fish had open wounds. Just like us when we have a break in the skin it scabs over so do fish just very slowly a fishes slime coat is what helps to keep the blood from going into the water so it can clot.

I would not poor that stuff on a fish it would more than likely cause troubles for the fish. Do you have corals i the tank and if so what are they? also do you have an urchin?
the black could also be coral burns or even a urchin quills could be in the fish and the shaking could be because he is trying to get them out.
I don't know for sure we do need pic's and answers. I say coral burns because my clowns that host a couple hammers get them from time to time and they can be fairly large burns some times with white spots. It looks bad but it does not seem to affect them any.
Bill