Is it a drastic change, or something that's being going on gradually? I've heard of quite a few bettas with curled fins and nothing was wrong with them at all. It was just the way they aged.. maybe like wrinkles on a human
its not drastic it doesnt seem to bother him it looks almost like an ingrowing hair its a tight curl at the tip. Id say it happend gradually and he doesnt seem impaired in any way