Zoa eating nudi, which is bad, bad, news.  My whole tank ended up in the dumpster because of those things.  If you only have a few zoa's in your tank, and you can remove them, you should be able to get rid of them.  I would suggest setting up a small tank and putting all of your zoas into it, and treating the zoa's separately, and letting the nudi's die off in your display tank for 6+ weeks.