I use the
Reef Crystals by Instant Ocean, becuase of elevated Calcium and
Magnesium levels. I drip Kalk to maintain Ca/Alk levels and will add a little C Balance to bump them up....Works well for me.
To get the tank started, use what you have.....When it's time to buy more then consider what your plans for the tank are (corals if I remember) and start using an appropriate salt.
I think IO and Oceanic are a couple of the more popular salts because of price and consistency (although bad batches can happen). I am really wanting to try the Tropic Marin Pro salt, users swear by it....it will cost about 10 cents more a gallon from the others.
I think for now, use what they gave you....when its gone and you've read a bunch of threads on salt, make your choice.
Good luck w/ the new tank, keep us posted with Pictures!!!