which sea salt mix to choose?

[Matt]

I started with Red Sea, which has been fine, and I don't have any problems with it, except that it hasn't always adjusted PH really well. I have been reading a bit on this topic lately, and it is a storm of information and misinformation. IO, Reef Crystals, and Kent salts are all made by the same manufacturer (Aquarium Systems), and apparently test very similarly.

Red Sea has had many reported quality control problems.

Tropic Marin is widely regarded, but expensive.

Shimek published a study that recommends Marinemix, which Fenner dismisses as junk (along with Shimek's analysis and methods). and instead suggests Tropic Marin is the salt to use, or IO if you can't get/afford that.

The much discussed s-15 report done by AquaCraft used a well-established lab to look at a bunch of salts and found all but theirs seriously wanting. but although their conclusions have been challenged, the science hasn't been (or at least not that I've found). In other words, the analysis seems to be accurate, even if the interpretations must be considered seriously self-serving in how they assigned the "scores".

Instant Ocean has scads of hobbyist's anecdotal support, and that's hard to argue with, but very few (none?) of us have the ability and skills to actually compare results fairly between brands. The popularity of any given salt is likely more related to the price and availability (marketing, IOW) than it's technical merits.

So... take my advice, and do what you want.