Awhile back, maybe 10 years ago Ron Shimek posted on Reef Central, some research he had been doing on how most major brands of commercially prepared salt mixes added heavy metals to our reef tanks and that these levels continued to build up causing harm to our corals.
He also sampled a variety of salt mixes to see what levels of heavy metals were in them. Bio-sea marine mix was the only salt he tested that did not have any levels of heavy metal in it.
Being relatively new to reefing at the time, I ordered some right away and when it came, immediately did a fifty percent water change with this new salt. Within a week most of my corals were dead!! This was most likely because of the size of the water change I did and not the salt, but it was enough to scare me off it for good. I also remember seeing posts from others at the time, experiencing corals dying off after doing a water change with this salt.
Anyway, just mix up a batch and test it for alk, calcium and magnesium. If the numbers are in the ballpark try a 10 percent water change and see how things go.
Good Luck!