Green Terror Injured

I think my Green Terror was injured but I am not sure. He has what looks like a cold sore at the base of his top fin on the end closest to his tale. It has been there for a week or so. He is alway hiding, he eats but I almost have to hand feed him, he wont go near any of the other fish unless he has to. Otherwise he looks healthy, color is vibrant and he has no problem swimming. Is there anything I can do for him?

Is it possible that another fish has injured him? What is the ph, ammonia, ect in the tank.........Are the other fish behaving normal?.............The lesion can be from several diseases all of which can be treated with an antibiotic.....I would be reluctant to use a med in the tank if all the other fish are well.....

Go to the drug store and buy a small cheap bottle of mercurochrome......Get someone to help you...Net out the fish and hold it firmly where you can access the sore....Use a q-tip to put a thick coat of mercurochrome on the sore.....Put it back in the tank and watch it closely......You might have to do it a couple of times to get it to heal........Be very careful not to get any in the fish's gills or eyes.

If you feel you must med the tank, use Maracyn or MaracynII exactly per the instructions.

I believe he was injured by another fish. He's kinda big so me netting him and holding him will be interesting but I will let you know how it goes. I will try to get a picture up before I go to the store. I have to find the cable that connects my camera to the computer. Thanks for the help!