FWIW, I have seen necrosis develop nearly over night and cutting frags didn't help, seems once the colony is 'infected', its a done deal. Not to say it isn't worth a last ditch effort. Too much flow will cause polyps, shrooms
, zoos and the like to recede in my experience. However, from my personal experience with my local reef club, there tends to be a culprit in the tank who may have suddenly found a taste for zoos. It may be worth QT'ing a colony or two to see what happens. Another thought is to check ALK
levels, Iodine and Nitrates, if you have the tests handy, as well as SG
and temp. I have noticed my zoos are not crazy about the summer months and the warmer water.