I just did my first water change using E.S.V. B-Ionic Seawater System Salt Mix. This system was fairly easy to use and dissolved completely. You basically mix the 4 components into the volume of water desired and you are good to go. My new water was ready in 15 minutes.
I've enjoyed using this product. Costly, but the salt is easy to mix and has absolutely no residue. My prep time for making water for water changes is now only 10 minutes.