Well this guy got over pop eye about a week ago. All was fine so I put him back in the main 150 gallon. I noticed this ever a knot on his head very large. IDK if he bumped something or what I put him back in the hospital tank hoping I didnt jump the gun but I added some melafix that worked for the pop eye. Any thoughts? I used the test strips and water is in perfect shape all other fish are fine