Fish Has A Red Patch On Side

[STEWARDSONS]

one of my emperor tetas is hovering with little motion and has a red patch on one of its sides.

any ideas what it is?

 

[KittyKat]

Water parameters, photo, more detailed description?

 

[loraxchick]

Is it being bullied by tankmates? Any other symptoms (any white/yellow patches, fuss or fluffy looking? flicking rubbing etc?
cheers