Are his gills inflamed or red at all? My fish has a bad gill that is really scarred from his time in the petstore cup ( his gill flap doesn't fully close on this side and it is really red in comparison to his other gill)... this is the gill he has bubbles come out of.
It doesn't seem to decrease his quality of life, tho. I just have to keep up on his water changes because when my levels get too high his symptoms get worse and seem to bother him. All in all, with a little TLC your fish will be just fine. It seems to be a fairly frequent issue with this type of fish and how they are kept before we purchase them.