Funny but those grew like crazy in my old tanks. When Elite gave me a 2-3 head frag it grew to a large 50+ head ball. I was fragging it left and right but eventually lost it due to heater issues. I don't think fragging 1 head is such a good idea. It is much harder for them to recover that way. Try to experiment with flow/light. I was also feeding them mycis shrimp which they liked a lot - which was surprising for a zoa and not paly.