I have a spare 20-25 gallon tank i got from my cousion. He had Reb Bellies in a few of his tanks. I think RB are schooling fish, right? How many can fit in a 20-25 gallon?
RBP's get up to 12 inches. That's the width of either of those tanks. You could keep a few babies in there for a few months, but in less than a year one RBP would outgrow that tank.