i would think low flow is a big cause to pox because whenever my zoas dropped on the sand bed and get swept to a hidden unoticable low flow area or get buried in the sandbed then poxs always appear , for mine temp and salinity are usually constant
so if you have a zoas that dropped or gets buried onto the sand bed , make sure you rectify it asap, for mine i noticed pox comes when discovered some frags that dropped from the mother colony and get buried , poxs usually will appear on those frags, thats y nowadays i always glue loose polyps to frag plus and put them in the qt tank or frag stand asap. due to my previous lazyness i have lost too much zoas, i also learned it the hard way. oh and i also noticed when i was running a ozoniser i dont notice poxs