I feel your pain. ;) I rescued a Petco boy almost a week ago...and he's still not eating. These are the things I've seen rec'd/been told to try:
- live food or regular food moved around with tweezers to tempt them
- pellets soaked in garlic
- blood worms or brine shrimp (they come both frozen and freezedried)
- flakes or pellets. Most seem more interested in pellets than flakes
- time to let them adjust
- and, betta can go almost a month without food. If he seems active and interested in his environment, he's just acclimating.
- make sure that he's going to the bathroom, if not, then you might try an epsom salt treatment just to make sure that he's moving along and that's not the reason he doesn't want to eat
If it makes you feel any better, my rescue boy Geoffrey had serious ammonia burns, but he's recovering and flares at his neighbor, swims around a bit, and doesn't clamp his fins or seem to have any other issues...he just refuses to eat. It's making me insane. ;) If you want to rant about the not-eating, feel free to PM me, I can totally commiserate with you. ;)
Good luck to you, and I hope he starts eating soon! :)