First why would they put them in the SAME
cup? Your gonna put 2 SIAMESE FIGHTING FISH
in a VERY
small space and expect them to be little finned Mother Teresas? Ya right!
Stress Coat! This will reduce stress and I use it as my regualr water conditioner. It also helps with regrowing of fins.
Methylenen Blue wouldn't be a bad option. You should move him to a bare jar and add 1 drop of this to his jar.
Ampicillin: I keep this incase an infection occurs (which has only happened once in my fish room). Good on gram positive and gram negative. So I'm always covered :)
Hope he gets better :)