it depends on what kind of hammer: branch hammer or wall hammer? Also, what look are you going for in your tank? I like to let the corals get as big as possible before fragging them. My wall hammer is massive and I cannot frag it, so it will grow until it out grows my tank and I will have to figure out then what to do. I just fragged my branch hammer and it was because it was growing into the bubble coral. Up to you, good luck
-Doc