They don't get much bigger than a quarter at most. More often than not, they stay smaller than a dime. You have to remember that baby mollies are just a little larger than a BB. The molly babies thought the balls were food, would go bite them, and get caught. The adults stayed away from them. In fact, I still have a few of them in my tank. If you don't want them, just kill them as you see them, but don't let it get to you. The reproduction rate is nothing like that of Aiptasia. I would put it on the bottom of my "To Kill" list.