It really helps with infections since it has antibacterial/fungal effect. Also will help balance electrolyte level and encourage the production of lime coat,which will in turn help protect him form infection. But only when it needed and for certain period of time. So if he is acting normal now i would think super clean water and stress coat would help him, hopefully he will completely recover.
Also if you ever need to use aquarium salt again -You need at least 5 days rest between aquarium salt (Sodium Chloride) example: 10day on-5 days off-10days on...etc.....however, if you need a salt treatment longer than that you need to look for a different treatment or cause......
Also not sure if you know about Epsom salt also very helpful with buoyancy problems, constipation, pop eye, dropsy...The same instructions but you can use long time term and with chronic problem like sbd you can use indefinitely