I'm surprised more people aren't mentioning
ESV B-Ionic Seawater System. ESV is definitely my favorite salt and I've been using it for over 15 years. This is a high-quality salt that mixes clean and quickly. The concept of using 4 parts makes a lot of sense and eliminates precipitation issues. Each kit consists of two dry components and two liquid components. Dry NaCl is mixed first, followed by a Mg salt mix, then the two liquid components (one containing CaCl and positive charged elements; the other, the alkalinity solution with negatively charged elements. The two dry components dissolve in a couple of minutes and there is never any residue, just crystal-clear saltwater!
Other brands of salt have the problem of distributing a minute amount of trace elements throughout the entire bucket of salt. It is impossible to distribute them evenly. The ESV B-Ionic System solves this problem by measuring and adding each of the 4 components separately.
I had the opportunity to pass by Long Island 2 days ago so made a quick visit to ESV and stocked up on a good supply of salt. Here is a picture of Bob Stark (CEO) standing in front of a pallet of salt!
You can read about the ESV B-Ionic Seawater System here:
http://www.esvaquarium.com/