Thermostat Aquarium My Clown Loach Have White Spot Was Told To Add Aquarium Salt To My Tropical Tank By Pet Shop ,is This True?

My clown loach have white spot was told to add aquarium salt to my tropical tank by pet shop ,is this true? - thermostat aquarium

was told that I can not add the white spot treat? is that true? or will be in order, I can also put a bit of thermostat?