I agree that the tank is too small for that many fish. It’s not so much the swimming space as it is that a 6 gallon tank is hard to keep stable when you have more than one or two fish. A 10 gallon would be easier to keep stable. Think about like having a small house as opposed to a big one and all the stuff you accumulate. A big house is easier to keep organized and clutter free than a smaller house is. My four bedroom house is a lot more organized than my studio apartment was.
