I agree that three is max and by the time they are halfway through their second year they move to a wider tank as they should be 9-10 inches long by then. Even a single RBP will get crowded in a standard 55g around then due to the 12" width of the tank. A 50g (long) or a 65g with their 18" widths are much better and can house 3 for life but a 75g is even better.