Simon:
Craig Bingman and others have suggested that the high metals in synthetic salt mixes may come, at least in part, from abrasion of metallic equipment during manufacture. The same might logically be true for crushed coral, though I have no useful information one way or the other.
If these metals were coming from the crushed coral itself, I personally would not worry about it as the corals in the tank will probably take it out as they calcify. If they are coming from some unnatural source, then there might be more cause for concern.
I personally don't worry much about iron in skimmed reef tanks because I think it is quickly removed. I add quite a lot myself.
Aluminum is another surprisingly high one, and may be there for the same reason as the iron. OTOH, it has quite low solubility, and it may precipitate even if added to a reef tank in excess. It may never solubilze in a reactor. Could there be enough to be a problem? I have no idea.
Nothing else stands out to me, but I've not spent a lot of time thinking about all of the ramifications of every metal.
Greg would be a better one to answer about availability and such. I've only seen the half ton of limestone in his driveway!
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Randy Holmes-Farley
