I am about to get two oscellaris to begin my broodstock tank. I am going to let them change sexes in my frag tank until I get my system built. Would it be better to buy a medium and an x-large and add them to the tank or buy two mediums and add them to the tank? I would think that in the first situation the x-large would become the female since it would be dominant, but would it kill the other clown?