Help With My Sterbai

[Aleksandar]

One of my cory sterbai has some black bubble on the bottom of the body, between the front fins. Does someone know what is it?
Thanks in advance

 

[Byron]

Any chance you could post a clear photo?  Might help someone to ID the issue.
 
Byron.

 

[Aleksandar]

I cant post clear photo, it's not showing the belly plus is hiding most of the time

 

[Lillefishy]

Without a pic it's almost impossible to say what it might be.
Is the whole area black, or is the black underneath the skin?