I've heard so many people say so many different salts...
I use Tropic Marin.
I think the three most popular are Reef Crystals, Oceanic, and Tropic Marin. You can't go wrong with those.
At first i bought IO, and always had low cal....below 300
started using Oceanic and i have high cal....above 500
i think i might use reef crystals or tropic marin next.