In my experience, if you have one type of zoa that is really outpacing the others in growth, you will likely end up with a rock full of one type, with a few others sprinkled in if you're lucky.
Fortunately, fragging zoas isn't very hard. For fragging polyps on an established piece of live rock I like to use a combination of a box cutter/razor blade and an old butter knife (seriously). I've found that you can sort of pry up underneath the zoas mat with the butter knife (you will basically scrape up a little bit of the surface of the live rock, keeping the mat intact). Then simply cut between the polyps (or straight through some polyps if you don't care about losing a few) to separate what you have cut off into smaller frags.
All of this said, BE CAREFUL. Palytoxin while being a very rare issue, can potentially be life threatening. Don't disregard proper PPE when fragging any coral, but particularly when fragging zoas/palys. Hth, good luck!
