Three days ago, I got a new betta named Regulus. He's a lovely halfmoon male and he was quite healthy and energetic since the store had gotten a shipment just the previous night, so he hadn't even been on the shelf for a full day. In the car, he was so energetic! My sister was holding his cup and he was swimming around and flaring at her hand.
I put him in a 2.5 gallon tank that's both filtered and heated and he immediately went and hid. I figured he was just getting used to his new home. When I fed him and he didn't come out to eat, I just assumed that he'd been fed at the pet store and wasn't hungry. But now, three days later, he still hides all the time. Most of the time, I see him in a little cup I put in to be a cave. If he is out, as soon as I take the glass cover of his tank he darts to find somewhere to hide. He doesn't even come up for food and only eats if a piece of food happens to sink to the bottom near where he's hiding.
It's not like being picky can be an excuse, either. I've given him pellets, flakes, FD krill, and FD blood worms. Nothing has been able to tempt him out of hiding... Should I be worried?