My Platy is swimming weird

[malu]

Hey so basically i got my Platy fish today i went to the worlds biggest pet store which is in germany and they had tons of fish so i got myself 2 platys and 1 guppy. I already have 4 guppys so that makes me have 7 fish now. My problem is my one Platy i got today got nipped the entire 1hr car drive by the other platy. Before i put the fish in the water with the other guppys i ofc tested the water of everything and everything was in a normal state it was just perfect for the fish. Basically the fish swims kinda half on its side, i made a video so yall can check it out and maybe help what the problem is

I have a water pump that came with the tank so i dont know anything about the pump since im pretty new in the fish game.
I'd love to hear what it possibly could be. I'm really worried about that fish

 

[Delapool]

Hopefully just stressed - any improvement?

 

[malu]

swimming normal again but his back fin is loosing colour. his back fin is see through and not orange anymore? is it because other fish are nipping him?

 

[Delapool]

Sounds like it. I've had them die from being picked on.