FWIW some of my zoas showed up with white patches on them and I thought I may have had zoa pox. Eventually they went away, the only thing I did was a freshwater dip (for other pests not the pox). I don't think either of us are qualified to really make an exact diagnosis as to what exactly the white patches are in both of our cases so it may be something totally different but just so you're aware it may not be a major problem. Have you checked (and doublechecked) all of your parameters, especially calcium/alkalinity/magnesium/salinity (with a calibrated refractometer specifically)? I've noticed my zoas close up when my alk drops or when my salinity rises.