I don't know the exact size of his tank, but I would guess it's about 1 gallon or so. Maybe 1.5. I don't know the water temperature, but he has no heater, so I'd guess it's too cool for him. The tank has been running for 3 days. He has an air flow, bubble-making thing, but no filter.
I know he doesn't have everything that he needs (I'm new at this), but I'm going to upgrade him to a bigger tank with a heater and filter hopefully tonight. I'm worried about stressing him out too much though, so I don't know if tonight is too soon. I just bought him and put him in the tank he's in now a few days ago.