I've used 3 different brands.
Oceanic. Decent stuff. Never had a real problem with it though I did fight a bit with
pH. Great
calcium levels.
Red Sea. I'll never touch this stuff again. Had a big hair algae outbreak which I'm still dealing with 9 months later (though slowly winning). In talking to other people, a lot of others have had similar issues with this salt mix.
Seachem Reef Salt. Top notch stuff. Great for keeping corals. From everything I've heard, they take quality control really serious. This is the salt mix that I'm currently using.
Also Seachem is currently releasing a new brand of salt called
Aquavitro. They actually post on the bucket exactly what the specs are for each element from the batch it came from. One of my local
LFS's is getting the stuff in the next week or so and I'm going to be getting a couple of buckets. Keep in mind if you have a
FOWLR tank, then a salt mix like this is overkill.