Looks like someone took sandpaper to my corals....why?

[Chrisjbarry]

It looks like low alk, I just had this happen to me. When running low nutrient system it seems to do this to my corals. If I raise up the alk to 9-9.5 cal 425 and mag 1350 stops this issue.

 

[Bigcefa]

I wouldn't rule out a bacterial infection of your corals which often gets over looked when people have these kinds of issues and can't figure it out

 

[Bigcefa]

Did you figure this out? What's your fish list?