I don't... I never have. I only use salt if it needs it for medicinal use. I have always used solar salt bought from Lowes. The "aquarium salt" from the petstore is the same thing, just ground finer.
There are some people that keep africans that will use salt, such as epsom salts and make a buffer, but even when I kept africans, I didn't even do that.
I find myself only really ever adding salt to my koi tank now a days- and that's because any little bump will cause an ulcer on them. They are way sensitive.