It does look like the beginning stages of zoa pox. From my experience it starts at the base of the zoa and spreads from there. Look at the base of the zoas in the left side of your pic. They look "pinched" and like they are starting to deteriorate. The phew whitish bumps are a sign as well. Those zoas also look like they are stretching really bad for more light. What kind of lighting do you have?
go to zoaid.com and they have an article how to treat zoa pox if it gets any worse.