I've got a Betta and I'm treating him for fin fungus right now. It's a huge pain as he seems to have the kind that's pretty resistant. I put him into a medical tank only because I was having to treat for so long and he was in a tank with a split divider.
The other Betta came with the fungus and mine caught it from him. That Betta has been completely cured (has been for months and now has huge fins).
Basically, I have to use meds at this point because he's got a really bad case which isn't responding and all the Betta websites say you have to increase the dosage and do multi-drugs if the fungus is really, really bad. I think it depends on the situation really. Mine injured his fins and that led
to the fin fungus.
I don't use products like Melafix only because I've seen too many postings that they don't really help, plus I read Betta's don't do well with them. I have used Kordon's Rid Fungus and that seems to help during the treatment. I found it at Petco and it helped with getting rid of the initial fungus.
My water is really good - change it regularly as tank is smaller. He just seems to have a bad, bad case.