Several days ago I came home after being out of town for a week and found that my female convict had a sore on her right side, just before her caudal fin. At first I thought that she'd hurt herself and that it was a section of cartilage sticking out and it reminded me of the "scalpel" that tangs have. I was finally able to move her into QT last night and since then I've noticed that the tissue sticking out looks softer, kinda pink and squishy. I'm not sure if she got hurt in the process of moving her or if something else has happened. The area around this spot doesn't look bad, I can't see any swelling or other problems problems. She's also shown no interest in food. Unfortunately she's doing a good job at keeping that side hidden so these were the best pictures I was able to get.

I started to think that this might be an ulcer but I don't see any examples that have tissue sticking out of the wound. Don't think it's a parasite as none of the descriptions of external parasites that I've found match what I see on her. She's the largest, most aggressive fish in my tank (angelfish, Bolivian rams, black skirt tetras, tiger barbs, cory cats, and a BN pleco) so I doubt this is the result of a fight. Water parameters are all good and the temperature is around 77. Because we have very hard water in my area I use RO+DI water for my fish.

As I said above, she's currently in QT. I'm treating with aquarium salt and Maracyn Plus in case it's a bacterial or fungal issue. Does anyone have any ideas what happened and how I can help her?