if it is an infection they typically spread, in my experience, so I usually frag ones far away from those that are showing the stuff. I don't usually take the next ring of polyps either, just in case you want a buffer so you know it hasn't spread to your new frags. Might be unrealated but this always seems to happen with ones that I have got at meetings...may traveling hurts them, I have no idea, but if left alone what I am describing will destroy them all on that rock and can also spread to ones that are close enough to be touching. My really wasn't rings though it was more like a white slime, so I doubt we are talking about the same thing, I just wanted to put this out there since you are keeping zoos.