i have a saratoga fish which has gone of its food 6 days ago and has some fin rot?

[Steve]

everything has been fine all i did was put catfish with it and it got stressed took catfish out still swims tried aquarium salt with melafix did 20 perc water change today and was told to add epsom salt couple of teaspoons fins not looking to good was getting ready to move into bigger tank but do not want to move till better in 380 ltres now was happy in tank no problems all started with cloudy eyes cleared up when catfish was removed but fins went of colour then slight rot then used melafix for 7 days help please also he is 34 cm cheers