New clown flashing - disease or aggression?

[MNscoe]

Newbie here. Bought 2 small clowns and a Tang from LFS, put in 29gal QT a week ago (were in copper so I’m continuing copper). Clowns came from new batch of about 12 at LFS.

Slightly smaller one always swims with dorsal up (see pic) and is spasming/flashing occasionally (video clip). Freshwater buddy says may be aggression/defense, not disease. I have no clue.

What do you experienced folks think?
Do I need to do anything?

 

[dinosaur_1552]

Perfectly normal, thats bonding/pairing behaviour.