How old is your tank?
Check you water parameters, with Ammonia and PH at the top of your list.
Is he the only fish having problems?
If the fish is still eating, try an additive in the food like Selcon. If he is healing from an injury it will help.
http://www.americanmarineusa.com/selcon.html
Products like ImmunoVital will help the fish's immune system too.
http://www.marcweissco.com/freshwate...uno_vital.html
Ken - BWA