FWIW, I stopped using Epsom Salts -- every time I dosed, I'd get a cyano outbreak from the sulfur (Epsom Salts are Magnesium Sulfate). I've since switched to Magflake (Magnesium Chloride). Unfortunately, now concern that the 'reef safety' of Magflake may be dropping... something about the manufacturer using potentially harmful ingredients or something. I don't recall all the details, I'm sure someone else does ;-)
I'll switch over to Seachem Reef Advantage Magnesium when I run out of Magflake.