Zoanthid pest ID? Black, overtook polyp, small black hairs

[jbh]

I received a Zoanthid frag from an online retailer a few days ago.

 

Dipped everything in a Bayer solution.

 

Had everything on a frag rack for a few days for observation. DI don't notice the affected zoa frag.

 

Placed corals, and the next day noticed one polyp that seemed to be engulfed by a black hairy pest or disease. The polyps adjacent were either not open, or barley open. (See photo)

 

I have removed this piece, cut off a couple of the seemingly unaffected polyps, and glued them to frag plugs to try to save a couple. Discarded the rest.

 

Based on this info, should I be concerned about this spreading to other zoas or corals in my tank?