The guy at the lfs is trying to make $$$. Your salt mix has all the same “Essential Elements” and all you are doing is adding to it. Even dosing at the “recommended dose” could add more of what is actually needed. Also this should not be used as a PWC replacement.
This is what it contains:
Contents:
Inorganic mineral salts of aluminum, boron, bromine, calcium, chromium, cobalt, copper, iodine, iron, lithium, magnesium, manganese, molybdenum, nickel, potassium, selenium, sulfur, strontium, tin, vanadium, and zinc in a base containing deionized water and EDTA.
Note that copper is being added and that none of these elements are listed in ppm quantities. I assume you haven’t spent $300+ for test kits which means you do not know what level of elements are currently in the tank.
NSW contains very little “trace elements” and as I said before maintaining ca/alk is usually about the only thing you have to add to a tank depending on how much coral you have.
What corals do you have that made the lfs recommend adding supplements for?