Personaly I like bio-wheels, they allow anarobic bacteria to form. What that does I couldn't tell you but it allows a whole lot more of it to form then any other system. I'd say get the bio-wheel or the largest tank you can get, bigger is always better.
Keep in mind a betta doesn't need a heater although the other inhabitants you decide on may need one. It can be tough finding good tank mates for bettas as most often your going to get aggression one way or another, either from the betta or towards the betta. I've personaly seen a betta with guppies as well as rummy nose tetras. Niether attacked the betta though the guppy fry became dinner.
|