I too see mucus plugs and with size of dots - Marine ich
That does look like marine ich, Cryptocaryon. Purple tangs also get benign mucus plugs, but see how some spots are on the fins? That is more a sign of ich, so is the rapid changing number of spots.
Your course going forward is going to be complicated. You won't be able to treat with copper or hyposalinity in that tank (I can see that one Zoa at least). That means you would need to move all of the fish to a treatment tank - no small task!
The number of spots may put you beyond the "ich management" stage, where if you keep the stress really low, and use really powerful UV, and siphon off the sand early every morning, you might be able to get this to go into remission. What people don't realize is that the ich trophonts themselves are stressors and something called propagule pressure comes into play - where no matter what preventative steps you take, the disease progresses to the acute stage; the spots increase, the fish stop feeding, develop secondary bacterial infections and then die.
