What could have damaged my maxima?

[In to deep]

I have a 75 gallon, with two clowns, two firefish, mandarin. Also a couple of peppermint shrimp, emerald crabs and the usual clean up crew. They have all been happy for a year! I bought the set up water and all from a friend! Parameters are great! We just added a tiny blue hippo, is he the culprit!

It's a tiny piece missing hopefully you can see in the pic!

 

[TriggerThis]

Doesn't look like an attack would be a perfectly smooth even section. I don't think he is the problem

 

[In to deep]

I wish I had more info! He was not like that last night!

 

[skinz78]

I'm thinking possibly stung by the Aptasia on the side?

 

[In to deep]

I need to treat! I hate those things!

 

[TriggerThis]

Be carful treating anything with that clam in there

 

[pecman347]

Be carful treating anything with that clam in there

+1 definitely