Take it back!! You can "kickstart" your biological filter by simply adding a raw cocktail shrimp to the water or even some fish flakes. Once they start to rot, your biological filtration is starting to be created!
If you are new to the hobby, lemme get to you before any salesman or catalog does...
You absolutely positively do not need to add anything liquid to your tank until you get filter feeders like feather dusters, then you can "feed them".
All the additives and supplements you do not need to add. And if there ever comes a point where they would benefit you, then you are well into the hobby enough to understand what you are adding and why you are adding it. But right now...nothing!
Salt water is the only liquid you need to be concerned with.