Eek! Help please!

This morning I noticed one of my Angels looks like his side was rubbed off.
It's on one of his sides and it ALMOST looks like theres a little bit of fungus on the patch thats "rubbed off"!
Any ideas as to what this is or what caused it?
We have been treating for ich, and I apologize but I don't have my water parameters at this moment.
I will post a pic and my water parameters as soon as I can, but I wanted to see if anyone knows what it could be?
Thanks everyone.
-Emily

Thanks, I was looking at it again and it almost looks like it has been picked at.
It's still eating and I haven't noticed any problematic aggression between my Angels.
We're testing water now.