Most people usually dip their zoos in Lugols Iodide or in freshwater. Actually the last time I was at the LFS where I buy all of my zoos from I asked him about this and he said that he just normally runs them under tap water. At first something just seemed wrong with rinsing with tap water but he is an expert in zoanthids so I came home and rinsed off my new zoos under the tap and had no problems at all. Seems kind of weird but it worked.
The main concerns for dipping zoanthids is the intorduction of zoanthid eating nudibranchs or sundial snails, not to mention other potential parasites or flatworms. Sundial snails are easy to spot and will consume entire colonies rather quickly. Before introducing any zoanthids to your tank get a flashlight and check your zoanthids for sundial snails or anything else that might not look like it belongs.
Luckily I've never had to deal with the dreaded zoanthid eating nudibranchs. I have only found one sundial snail in the past. Sundials will not readily produce in the aquarium like the nudis will.
Here is a photo of the sundial snail I found a while back -
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