Its hard to say exactly what to do when we don't know whats causing the probs. Could have been an injury, disease, even water parameter although I kinda doubt that.
I'd leave him be for now; just keep the water pristine, the lights low and reduce stress on him as much as possible. I hate to recommend meds without knowing what the prob is. The wrong med can be worse then no med at all.
aka Cycling Guru and the Ich Slayer
*glares at Terry and QTOFFER*
Card carrying member of FTAS & GCAS.