just today I noticed my celestial( in a 55 gal tank w/ 2 ranchus) was doing this semi-sideways drift/ swim and on closer inspection i noticed one gill does not seem to be opening.I have been treating the tank w/ Melafix (5 days )since my small ranchu had a white spot on tail ( almost gone ).I tested the water ammonia -0ppm,Nitrate- .25ppm.This is a fairly new tank 3 weeks(bio-filter 2wks old). I did a20 % water change today,prior to noticing this .I added aquaium salt and used Stress coat to de-clorify.I also noticed he is missing a few scales.Any suggestions ,does this sound like a sick fish or sick tank?