Hi, What a beautiful blue color he is! Wow! Magnificant! I'd say for a one gallon tank - the water could be changed completely in this circumstance even more often - like every 3 days if he still has fin rot. Betta fix is pretty good for fin rot usually if that's what he really has. Yes, the 80 degree water temperature is usually used more often during sickness and treatment of the fish in a hospital tank. Keeping the water at a slightly warmer temp like that also can cause bacteria to grow more rapidly and thus require full water changes more often. They are tropical and so they do like it warm, though. If you can't get to a petstore, can you order something online and have it mailed to you overnight, maybe - or have a friend or a family member who is near a petstore go there for you or give you a ride there or something like that, maybe? You know, I mean, if it's an emergency. I really hope your little sweetie is doing better.