Id like to Quote Mr. Randy's reasoning on choosing a salt mix which I agree with 100% :
"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)."
so at the end comparing IO and TMRP :
IO ca : 400 PPM KH 11 Dkh mg 1350 PPM
TMPR : ca 450 PPM kh : 8.5 Dkh, and mg at 1380 PPM
(my personal testing which matches the info on chemistry forums sticky thread)
so I prefer the lower KH of TMPR and hence why I do with that one. (although TMPR lacks K+, but I dose that myself, test kits wont show it, but I get better results when I add 1 ml of K+ to the new mix)