How often to add aquarium satl and stress coat solution?

You shouldn’t have to add any salt at all, unless you are using it for a specific disease treatment. As far as the Stress Coat goes, if you’re using it to rid your water of chlorine, that’s fine, just use it on new water going into the tank at water changes. However, you do not need all the other stuff that is in Stress Coat - there are other less expensive products you could buy that would dechlorinate your water. Also, make sure you know whether your water contains chlorine or chloramines. Phone your water utility or go to their web site. Note, if you have chloramines, that although Stress coat says it “instantly removes chlorine and chloramines”, it’s a little misleading. It only breaks the chloramines bond, you will need something else to detoxify the ammonia from that broken bond.

You should also bump up your water changes to once every week... it will work far more wonders than aquarium salt .