I agree with Randy's response to which salt mix one should use (This a quote of his comment):
"I do not think there is a "best" salt mix. Nearly all of them will work fine as long as you know their pros and cons.
I personally prefer Instant Ocean, and this is why:
I don't want excessive borate, which leaves out Seachem.
I don't want vitamins or anything else organic in my mix, so that tosses out some like Reef Crystals, hW Marinemix Plus BioElements, Kent, Coralife, and Nutri-SeaWater.
I don't want excessive calcium (long term use of limewater as I use drives up calcium, so I do not want it starting high), so that tosses out a bunch, such as Kent, Seachem, Coralife and Oceanic.
There are certain companies that I will not support due to their misleading claims and/or product lines. That tosses out a few which I won't detail here since it is my personal thought as opposed to a specific issue with their salt mix.
I won't use certain lines of natural seawater due to excessive metals in it.
That only leaves a few to choose from, such as Instant Ocean and Tropic Marin Pro. The remaining ones might all be fine for me, but IO is lower in cost, especially if you get it when it goes on sale (which it frequently does)."