I got this frag on Sunday. I did not notice the growth at the LFS. I did a Lugol's dip and put it in the tank. Yesterday I noticed the growth on one polyp in that place. Today it is the same size, shap and in the same place.
it could be part of the zoa, maybe some type of wart or defect/morph? I have never seen anything like it. Try using RC.....Reef Central, they might have an idea of what that is.