I dip all zoas in Lugol's and FWE. I have recently experimented by putting a drop of FWE on nudis that I manually remove and put in a cup, There seem to be 2 varieties. One variety is not affected at all by it, the other literally drops dead within seconds. Now that's one drop in1/2 a cup of water. I am not sure what kind of dosage it would take to rid a tank of them.