My husband and I have two saltwater aquariums, a 135 gallon and a 37 gallon. We use Oceanic Natural Sea Salt Mix (for making 90 gallons, which is 26.1 lbs) which we purchase at Petsmart for about $34.00.
This sea salt does a very good job of keeping the water in the proper proportions for our saltwater fish. It contains calcium and natural trace elements, comes in a resealable jug to keep it moisture free, and creates a healthy environment for the fish. This sea salt uses micro-crystal technology which provides for increased water clarity, rapid stabilization when mixed with water, and reduced algae growth due to the absence of nitrates, phosphates and ammonia. It also has natural buffering action with KH stabilizers.
We use well water in five gallon jugs, so we have to measure out a certain amount of salt to go in each jug, and the jug has to be shaken up (my husband's job) in order to properly disperse the salt in it. The only negative I have found with this salt is that it seems to take quite a bit of shaking up to mix thoroughly in the well water, and sometimes we will still find some salt lying at the bottom of the jug. I don't know if other salt mixes would do the same, but with continued shaking, the salt does mix in. We do like the Oceanic so we have been using that on a regular basis for our water changes in our tanks.
Overall, I would say that the Oceanic Natural Sea Salt Mix is a very good quality salt for use in saltwater aquariums.