Originally Posted by
Altenweg
The usual rule for fish is 1 gallon per inch. So, if you have a fish that's 5 inches long then you need a 5 gallon tank and can't add anymore fish.
Betas fall into the 2 inch category but are not very active fish. Still, I find it cruel that many people think it's okay to keep them in tiny little bowls, even cups.
My dad had a 30 gallon tank with many different fish, usually Neons (also betas) and angel fish, etc. etc. He always had a siamese fighting fish in the tank and there were never any problems.
Just keep to the 1 inch per gallon rule and you should be fine, but take into account the growth of the fish you buy. Ask the store how big they'll get before purchasing. :)