There's a good article on the contents, both good and bad, of various reactor media in one of th old issues of reefkeeping magazine. Unfortunately, ARM, like many of the commercial media, has some elevated levels of heavy metal contaminents. (I don't mean old Ozzy Osborne songs) IMO, a really high quality media has yet to be marketed, although there's probably something out there that I'm not aware of. I suspect that this issue will become somewhat like the the salt wars of the past few years.