I just use a small amount of salt, that I have always used in all fresh water aquariums. It helps build the slime coat, and repel parasites. Around 2 teaspoons for 5 gallons of tank.
I use aquarium salt, 1tsp/20g as a slight preventative to infections from small fin tears, scratches etc and only add more after every technical 100% W/C (say 10g/week in a 100g, I would add more salt after 10 weeks.)