On my way out the door this morning I noticed a mark on one of my yellow tangs. I was in the tank last night rearranging some stuff at 11pm and I know the mark was not there. It was early this morning, so the Tank lights were not on. The only light was the natural light coming in from windows which wasn't alot as it was early and over cast. My yellow tangs always get pale during lights out, but I've never seen a spot before... Thoughts???