RE: Why do stores keep Betta fish in small containers?
This isn't directed at OP, I'd just like to point out that some of the posters are a tad dramatic. I'm sure a 5 gallon tank or more is ideal for a betta, but it will not "die in days" if it is in a smaller tank. For my first betta, I (being uneducated ) kept her in a decorative bowl without a filter. I cleaned it regularly, fed her pellets. She was active, moved homes with me without a problem, always had bright colors, lived for 4-5 years. My house was usually about 70 degrees at room temperature. She was active, interactive, had a very high appetite, would blow bubbles upon seeing me. I would regularly bring in water samples to the store where I bought her food, and have it tested. I was always told it was among the healthiest levels they had ever seen.
You do not need a massive tank to have a happy betta. It is ideal for exercise, balance, ammonia level, temperature control, and filter options, but your betta will not immediately die if you have recently bought one and do not have a tank yet.