White spots on back glass

[Intense37754]

I searched and found a lot of post on these things, still not sure what they are but when I clean them off it feels like sand paper.
really interested in removing them for the sake of removing but curious as to what it is a what will eat it?

If a wrasse eats them what kind and there’s already a cleaner wrasse in there that I don’t believe have touched any.

 

[Omgitsjoe]

Bump