Water quality for him has always been good, if not very good. Temperature would fluctuate a little, but never badly. Had him since he was hatched...I bred his parents, raised him from an egg. He's...gee...6 months now, maybe. He was sick before the move...that's part of why I gave him up. I don't have time to treat him, plus I'm having to give up most of my fish, anyway (not for lack of care, but I'm moving, can't take them with me), so I figured it was the best chance he had, not only at survival, but at a good home, too.
Tank's not too small. I'm not sure of the exact volume of the container, but it was kept clean and it wasn't too small. Tank was always kept pretty well bare for ease in changing...lots of Bettas to go through at one point, and decor just made it take more time.
About...let's see...2 1/2 weeks ago, maybe, something like that, the fish changed tanks. Comparable move, was situated against the same female he'd been staring at for a long while (most of his life, actually). Same temp, same shelf. About three days before I gave him away, his fins started to look weird. They didn't look like finrot, they didn't look clamped. I added a small amount of salt. It didn't seem to do any good. I keep medications on hand, but I don't believe in using medication until there's a definite symptom requiring a definite, specific medication, to avoid waste of medicine and damage to the fish. He was still eating fine. No bloating.