In my experience, chemicals designed for reefs far out perform the raw ingredients. I'm not 100% sure why, but I think the reef manufacturers know something...like maybe that's why they add 'other stuff'. I think the 'other stuff' plays an important role.
I used to use Dow Flake, Mag Flake, epsoms salts, baking soda, etc. I changed to using SeaChem and Kent products (mostly), and I think my reef is much better off.