No salt mix is consistent unless all of the components are mixed just prior to use. Settling from shipping, and not mixing well are the reasons for this. Odds are that you won't get the same results from 2 samples of the same brand salt mix taken from different batches.
The only way you can be sure is by using a salt mix that must be mixed as needed.
There are a couple companies that do this.
I recall one called "get tanked aquariums"
Get Tanked Aquariums, bulk reef supply - Get Tanked Aquariums, bulk reef supply
Generally though, most of the salt mixes out there are fine to use. I got a bad batch of red sea coral pro before, and IO, reef crystals, and seachem, all leave a lot of filthy residue in my mixing barrel.
I like Oceanic, due to the larger bucket.