I recently had Monti eating Nudis and used a 15 min dip in Tropic Marin Pro Coral Cure (iodine) and lightly scrubbed the eggs off using a toothbrush and they have not come back...Obviously this is a little different type of Nudi, but I suspect that it would have the same effect on Zoa eating Nudis.
A quote for you:
"Very similar to the moni nudis as they pick up the color of the zoos as they eat. They lay eggs on the tissue of the column in a spiral pattern. Scrap them off with a toothbrush or tweezers as the clusters seem to stay together as you pull them off. You can dip for the adults fairly effectively, although at times they seem very resistant."
http://cmas-md.org/forums/archive/in...p/t-56605.html
One "natural" option that has been suggested is a wrasse as they eat Nudis Specifically the 6 line wrasse, coras and leopard, wrasse but again do more research as to what these fish are all about. The 6 line can be very aggressive, especially to other wrasse..