Not the most popular salt brand...I think it is partially composed of dried natural salt water. (I would prefer using a better tested and -safe and sure- brand like Instant Ocean).
I have used red sea salt with no problem, but prefer kent or reef crystals. I remember reading a thread about instant ocean having a calcium deficiency so I stay away from it.
I like Instant Ocean(IO, Reef Crystals or Kent...all made by the same company with slightly different receipes) or Tropic Marin. I stay away from Red Sea and Coralife