Adding salt to stingray tank

[Demon012]

I have a motoro stingray a peacock bass, silver dollars, African tiger fish and green sevrum in one of my tanks in my fishroom the ray got a bit of damage on its disk and I want to add some salt to tank, despite being in the hobby along time and having 10 tanks in my fishroom I have never needed to use salt, does anyone know if all these fish are okay with salt,, also the bit of damage on ray disk started to get a little black mark next to it, like a small stripe, any help welcome