If the male is old enough to breed and this his first time, leave him in the same tub a good 3 weeks or longer. Get another male for the other two. Sometimes it takes a while for them to get to it, once they do however they won't stop. Once my males and females reach about size for breeding I get them used to switching tubs frequently. I watch them closely to ensure mating is going on. Those who aren't used to being switched around or moved won't mate when change happens.