Water quality and high undissolved oxygen(air bullble) are the factors.
Find out what is causing excessive air bullbles in your tank, skimmer, overflow box, etc...
feed vegetables, food contains high vitamin C
Change water frequently, make sure you let the fresh water sit over night and circulate it with a powerhead. Raise the temperature to the exact samething as your maintank. In a situation like this, the worse you could so is to stress the fish further. Hypo or increase the salinity would both further stress the fish. Change about 10% of the water every three days for two weeks. HTH.