Betta do best in temps around 80 F. I would slowly raise the temp with an aquarium heater.

on thursday, I picked up a heater. the tank is slowly getting warmer. today, however, he took a bloodworm and then just spit it back out. any idea why he did this??

I don't know why he spit it out. At least he made an attempt. Maybe try live brine shrimp or flake food. Is he a little more active?

It seems as though we are all experiencing the same issues with our new Bettas. I purchased Berry (a blue Crown) and the tank (a clear plastic habitat tank) and accessories Monday at PetSmart. I came home, washed everything well, rinsed well, and filled the new tank (approx. 2 gallons). After the water was room temp, I put Berry in. He ate four pieces of food (the round stuff). He has not eaten since. This morning, the water was very murky and he isn't swimming a lot. This is not my first Betta (Morris lasted four years) but Berry is reacting so differently than Morris. I removed him from the tank this morning and washed everything very thoroughly again and recently placed him back in his tank. I called PetSmart and they said not to worry, as his stomach is only as big as his eyeball and he could go a couple of days without food. my stomach isn't that big either, but I can't go days without eating!!!! Any suggestions?

Is there any filtration going? Has the tank been cycled? Bettas may be air breathers but their own wasteproducts could be stressing them out, let alone new environs. Cloudy water could easily be indicative of good bacteria not bing able to keep up with the Ammonia.

The shopkeeper is correct in saying that they could go
without food for a couple days.

I know we all see individual male Bettas in small, glass bowls, but that's because many are brought in... and sold quickly and they can handle the small environment for a little while. They really need to be in a cycled tamk / filter, with a lot of hiding places.