Fins may be getting nipped by the other tang and progressing into bacterial issue.
Looking back at your video of all the fish, I wouldn't say your yellow fella looks terribly friendly.
My Tang likes to intimidate others very subtle like.. just sort of swimming under them or in their path or turning sideways to show how big he is.
Video was short so I can't say but I'd watch them closely. A fish going up to the corner sometimes means they are being bullied.
Looking back at your video of all the fish, I wouldn't say your yellow fella looks terribly friendly.
My Tang likes to intimidate others very subtle like.. just sort of swimming under them or in their path or turning sideways to show how big he is.
Video was short so I can't say but I'd watch them closely. A fish going up to the corner sometimes means they are being bullied.