What happened to my fish?

[Bob I]

Originally Posted by Bartman

Today I noticed that our Royal Gramma appears to have a chunk torn from her (we call her Emma) tail fin. She had no marks before today. Ours is a nano reef so not many possible culprits. What might have caused it? Oscellaris clown, cleaner shrimp, hermit, power head intake, sickness? Any thoughts?

TIA.

Just as a consolation, when I first got my RG, it also managed to get a torn tail. I never figured out who did it. It has grown back, and never happened again.