The salt is for nirItes, not nitrAtes. Salt helps fish (something about preventing the blood from hemolizing..clotting..I think)
Only thing for reducing nitrAtes is to waterchange, however if your tap water contains NitrAtes already, you can get a nitrate sponge to put ino your filter. It looks kinda like a tea bag.
amonia converts to NitrItes, then to NitrAtes.
amonia is most toxic, NitrItes, not as bad, but still need to be reduced if above acceptable level as per your test kit, and finally NitrAtes to which some fish species are more sensitive. Like Black Ghost Knifefish for example.
I hope it answers your question.
Once you see nitrAtes, your tank is about cycled, but you must monitor at intervals for a month or so afterwards. Finally you'll just need to watch NitrAtes after the tank is 'aged.'