Im new to this hobby and just got my first frag a month ago, but I have tried a number of different things with lighting and flow just to see what makes zoas tick. Im amazed at how just turning down the flow a little bit makes a world of difference. Perhaps things just arent the same as with your smaller tank. Im sure you have tried fooling around with flow and lighting, maybe intenisty is too high for zoas, just a suggestion, Im sure you know a heck of alot more than me about this, good luck buddy