His new tank came yesterday, and I ordered stress coat, new food, a filter and a betta hammock. I have to pay tuition right now, so I can't get him any plants just yet, but his moss balls have been in quarantine all week, so I think at the end of the 10 days of salt I might move him in with them in the big tank.
His fins lost all the weird blue and yellow coloration that they had while he was sick. He's all dark and his fins are completely open again. :) So luckily, his stress is gone, and there hasn't been any more fin deterioration in days.