I would keep him on the medicated food but switch the tank water treatment.
You can feed that food while treating with something else.
If you can get a good picture of his fins that are ragged or have the "spot", it would be easier for me to see what exactly it is?
How is the whiteness on his head? Did that disappear now?
I'm thinking maybe you should try Rid-Ich + by Kordon. It has formalin in it which will treat fungus plus any parasites.
It won't hurt the biological filtration. You add 1 tsp per 10 gallons of water and then treat once every 24 hours after a 25% water change. I wouldn't use anymore salt in the tank while treating and make sure to take any carbon out of your filtration before
treating. You can get this at Petsmart too.