My Copperband butterfly fish needs help

[Rowey]

I purchased this fish about 3 weeks ago and he was settling in quite fine, But 5 days ago I noticed he had stopped eating but still seemed physically fine. This morning however his bill appears to be reddish and he is constantley nosing it out of the water.
His diet prior to this was only mysis shrimp frozen foof and he was sharing a tank with a now breeding pair of black and white Osselaris and a blue star fish.

I have now placed him in my grow out tank by himself and according to my local fish store all the paremiters are fine.
I had an issue of my main tank being too salty prior to him becoming ill which has been remedied now but I have no idea of what illness he has.

He has no spots of any kind on his body and his eyes appear normal, The snout being an abormal colour and him not eating and poking his nose out of the water is quite worrying for me, any Ideas ?

Sorry Ijust realised ive posted this in the wrong place.