I changed the water yesterday, and I use tap water. Before I put him in the tank, I put a water conditioner in. I think he's a picky eater and that the water was too chilly. I put his tank in my bathroom, which is one of the warmest rooms in my house. He seemed to perk up after being in there all day. He did eat some blood worms, but not the pellets. Both are hikari brand betta food. I know the blood worms aren't the best food for him, but I don't think he likes the pellets.
I try to keep the water in his tank warmer, but I don't know if I should get him a heater. I don't want to boil my poor little fish with a big water heater, though I don't want to keep his tank in the bathroom.