The fish has Ich, if you aren't already using it, you need to use melafix ASAP! It's likely from you doing so many water changes, if you have been changing the water and the new water you add isn't the same temperature as the water he is in it can cause stress and stress is one of the main reasons fish get Ich, if you don't treat him soon he will die from it. Sometimes they are too far gone to help them, but you can always try. Also I would double check and make sure the doses of salt are the proper amount.. in the small bin you have him in you don't want to over salt the water.