it seems like it, do you use activated carbon in your tank? I've heard it is one of the main causes, in case you do remove it and do two consecutive 80% water changes to remove all traces of it, this should help. Other things that can cause it is Hexamita parasites, you may want to treat the tank for those, usually, activated carbon causes an increase of Hexamita parasites since it crates water conditions favorable for them.
in general, I would recommend
(if you have activated carbon) remove it and do the water changes
treat for Hexamita with metronidazole
and try to feed live and fresh foods only to your discus to help him improve and heal faster