One of 3 of my gulpers is not doing well. The other two are fine, but this one I'm noticing has damaged fins and lesion on the left side of his body. I think I also might have overfeed him because he was a great unbiased eater compared to my other two gulpers. Currently, I put him in a quarantine tank and put melafix and salt for he past 3 days, but it looks like he is still not doing well. I noticed occasionally he would open this mouth really wide or a while before closing it again. Moreover, I noticed him swim erratically flipping himself over with such force. Currently, he is vertically floating in the water. What else should I do to get him better?