a) what a beautiful frag!
b) those perfect circles? I do not think those are like the forams I have. it doesn’t look like they have any thickness. Could they be polyps but some look overlapping? I have an overgrown frag that has similar circles:
Weird! I do not have those on the walls like you. If you can get a closer view see if it looks like a snail shell like @H2OPlayar said. Are they on all of your corals and sand/bottom, too?