Ok, so the fish in my main tank were acting kind of strange, one Dalmatian Molly in particular. I did a 10% water change and a salt bath and they seem to be doing better, except for little Dot. I took her out of the main tank because yesterday she had these red spots, almost like little "blood blisters" (when a blood vessel breaks but the skin doesn't so it makes a red mark) on different parts of the body, the bottom of her tail fin looked like it was starting to rot, and the scales on the base of her tail were protruding. I put her in a 10 gallon tank I was going to use for a nursery. It's already been balanced so no need to worry about that.
I started her on some broad spectrum antibiotics that came with the 45 gallon that I was given by a friend of my aunt's, Maracyn-Two. I added two tablets to the tank yesterday and one today, as it says to do on the box. Today she was so much worse than yesterday. It literally grew overnight. She had this fuzz like stuff surrounding her tail fin and base of her tail, and the "blood blister" at the base of her tail looked bigger. I tried to take a picture of it to post here in case anyone could give me some advice. When I put my hand next to the tank to see if I could get her to move a little, she gave a strong stroke of her tail and half of her tail fin, a few scales from the base of her tail and almost all of the "fuzz" fell off. I also noticed that almost all of her scales up her right and left side are protruding from her body. She looks almost like a frickin pine cone.
I have a before and after picture below so you can see what I mean about the tail. I have no idea what to do. I have no idea what this is, I've never seen anything like this before. I got this fish 3 days ago from the pet store and none of my other fish are showing any of these symptoms. I've been watching them like a hawk, which they don't really appreciate, but they're all ok. I think she already had this disease or parasite or whatever it is she has, and the stress from being moved from the pet store and into a new tank threw it into hyper drive because like I said, none of my other fish are showing anything like this. Is there someone that can please tell me what to do? I'm having serious ethical concerns keeping this fish alive because I really do believe she's suffering. She can still swim ok, and she ate a little of the food I gave her earlier, but half of her tail fin is gone and some of her scales and the medicine doesn't seem to be working at all.