I've had my betta, Arthur, for a little over a month now. He is currently in a 1 gallon hospital tank kept at 78 degrees, no filter. He has been on 1 tsp aquarium salt/gallon for the past seven days, with 100% changes every day.
Not long after I got him his tail split, and then more fraying began to appear along with signs of mild fin rot. Seven days ago I began treating him for it with aquarium salt. Everything was going fine and the tears were starting to heal (though I've noticed that since I've gotten him his fins have curled a bit - his dorsal fin is curled over and doesn't really straighten out, even when he flares). The other day some new tears appeared. Today I went to check on him and the dorsal fin has a couple of new holes (seriously appeared overnight, I checked him when I did his water change last night) that are ringed with black and have some white spots.
Since I've already had him on salt, what can I do to try to fix this? I have not tested my water, but I'm planning to do so soon because the curling is starting to worry me. I have roommates who use the same water with the same conditioner and don't have the curling issue.
He appears to be otherwise healthy.
I attached a couple of images (I hope they show up!). In the first you can see his tail and how it's healing (the bigger slit used to be twice as long, it's healed super fast) and how the strands are curling at the ends, and in the second you can see how his dorsal fin is curled. It really doesn't change from that position much.