Fish people! I need help!

I bought a betta fish several months ago from Wally world. My daughter's room is downstairs and it seemed a bit too cold for him. Plus he was looking quite fat and we barely feed him. I read that in cool temps they have digestive issues.

WELL. I just moved him up in my room in a bright area, but not direct sunlight, AND....there are some creepy crawly dust specs looking things all on the sides of the bowl! What do I do??? Change water, asap, yes....call the vet? I don't know what this is! They aren't on HIM - that I can tell - but they are on the sides of the bowl.... They are long and thin and could pass as a spec of dust, but in bright light, I see them and they are moving.