Originally Posted by Sj45
Alright, I was just wondering because at the stores you will never see filters. I'll buy one, thanks.
It bears mentioning that pet store conditions ARE NOT proper care for fish. Pet stores provide the minimum amount of care necessary to keep fish alive until someone purchases them. Bettas are unfortunately enough to be both finicky enough about who they share a tank with to make them nearly impossible to keep in the general population, and tough enough to take the kind of abuse that leaving them in those tiny unheated cups is.
You can cram a man into a 4' x 4' x 4' box with only a tiny air hole and a dribble in a bit of food and water every day and he'll probably survive for quite some time. I don't think anyone will think he's happy about it.
All you have to do to see how wrong the idea of keeping them in cups is is to take one home and put them into a proper tank. My betta went from a pale faded blue and pink fish sitting on the bottom of his cup with his fins drooping to a rich, deep purple and red fish with his fins flowing as he swims around his tank.
As for a filter a sponge filter is a great idea for a betta tank. As are the smaller internal filters. Neither should cost you much more than $20.