Not sure what medicines would do for a stuck gill... I have one male, who kind of has that... Skull... His right gill seems to stick out more, and has a spot where it sticks out more than the rest, and it does look weird. But he doesn't complain
He could have been injured... I know my Shiloh took a bad beating to the side of his face before I rescued him. Being shipped, can lead to causes like that - or you never noticed it for pictures when the breeder sent them?
For medicines however, take the powder out. Divide it into 1/10, and use 1/10 per gallon
I used maracyn 2 this way.