Glowlight Tetra With Red Splotch?

[damanax]

One of my glowlight tetras has this big red splotch right near his gill. It's on his right side and looks a bit swollen to me. He's acting normal, swimming around with my other glowlights and eating properly. Could it possibly be an injury or should I quarantine him? I've literally had these glowlights for about 6 hours and just noticed it. None of my other 7 glowlights have this red splotch.
 
My tank is 65l, is cycled and the tetra are the only fish in it.
 
I'm trying to get a photo but he's moving around a lot and my camera isn't the best quality.

 

[damanax]

This was the best photo I managed to take of the little guy.

 

[KittyKat]

Check the ammonia, that is not far off from what ammonia burns can look like.
 
Did you drip acclimatise the fish?
 
(On an unrelated side note, take all the dead leaves off the Vallis: they will only rot and produce even more ammonia.)