Had similar issues that looked just like that, this is what I did; with a very soft (baby) toothbrush clean the surface brushing gently in one direction to avoid more damage, dip in Seachem Reef Dip, assuming everything else is ok; flow, lighting, etc. then check your Iodine. If using a Red Sea test keep levels at .06-.09. I dosed Seachem Iodide. The first picture was on 2/20/2020, the last 2 just now to show the progress. Hope it helps.