The majority of salt mix brands on the market today ultimately provide the same thing: they keep your animals alive.  Trace element levels are what set most brands apart.  Before using any new bucket of salt, calcium, alkalinity and pH levels should be checked to make sure they are well within acceptable ranges for reef aquariums. Always keep your unused salt mix in an airtight container. Over time moisture in the air can mix with the salt, causing it to become solid and calcium carbonate can precipitate out.