this doestn really help with the zoas, but i had a colony or green zoas that had a sponge growing over them. if you still have the sponge problem, dip the entire colony in the iodine, then let the whole colony dry out for like 15- 20 mins. then scrape off as much as the sponge as you can, swoosh it around in some iodine again and put it back in the tank. that helped with mine and i was battling it for awhile before i did this.