Re reading my previous response it came off rather abrasive, sorry that wasn't my intent. It appears to be or have been a water quality issue, in small tanks things can spiral rather quickly. Your parameters could've gotten out of whack between water changes. I still stand by my position of increased water changes to help him heal, I'm not great with meds so I don't have any recommendations to help with healing but I believe just good water will get the job done, keep us posted.