This is my husband's betta, Cookie Commander, who lives in my husband's office at work. He is a delta-tail and used to have a lovely, plumy tail and back fin.
About two months ago my husband called me to come visit quickly because "Cookie's entire back fin is gone." It wasn't actually gone, but it had lost all its plumy stuff (sorry, I don't know the terminology). There was just a spine sticking out of his back (or lying on his back, depending on the moment). At that point, I also noticed that his tail looked a bit like it had been pinked, or shredded.
We rushed to our most exotic of exotic fish stores and were told to buy BettaFix. We did, and used it as directed for two weeks, with no filtration and regular partial water changes. But nothing changed, and Cookie sat sadly on the floor of the tank. Plus, his butt-fin fell off entirely (not the plumy tail).
We panicked, so we went to a different fish store and bought Maracyn, and used it -- very, very carefully dosed, since he's in a small tank -- for a complete cycle. This stuff seemed to make him even more miserable. He barely moved.
When the antibiotics were finished, we gave him a couple days off, then resumed filtration, with occasional days of BettaFix and no filtration. He perked right up. He now lives what appears to be a normal betta life, greeting my husband when he gets in to work, asking for food, and swimming merrily around. The places on him that seemed like open sores are totally healed. But no fins appear to be regrowing!!
It's been over a month since the end of the medicine, and still no regrowth. Is this normal?
We're not fish experts, but I can tell you that the water is filtered bottled water, we have a thermometer to keep him at a good temperature (and a heater, although we've never needed to use it), and he's not over-fed. His tank is over a gallon and a half and has a decent carbon filter insert (I've wanted to remove the carbon, but I can't). He also has a bubbler when we're not using the filter.
Here is the happy, bedraggled fish!