Hi guys,
I should have been more specific above. All of the new CaCl2 from Dow (all of it since ~December of last year, the batch numbers begin with a "V" in the new stuff if I recall) has elevated bromide (Br-) in it. They have changed their manufacturing process and no longer strip the bromide out of it for any of the CaCl2 they now produce. For salt melter, that's irrelevant, but for us it's potentially a big deal.
The new Dow stuff has ~7,000 ppm Br- in it (~280,000 ppm Ca++). Bromide is one of the major ions in sea water (~67.3 ppm @ S = 35 ppt). However, bromide isn't necessarily removed very quickly in aquaria, hence it will build up over time if we are using the new Dow stuff as a calcium supplement.
For example, in a high demand tank a person might lose 40 ppm Ca++ daily. If they use the new Dow to replace that calcium, they'll raise the Br- by 1 ppm. If that Br- is largely accumulating, you can see that pretty quickly a person is going to have very elevated Br- relative to NSW. Assuming no loss of Br-, after 1 month Br- is elevated by nearly 50%, which might be undersirable. For that reason, it's not recommended that the newer formula from Dow (w/elevated Br-) be used as a calcium supplement in reef tanks.
Now, if it's a one-time shot and a person is using a Dow product to, for example, bump the calcium up in their salt mix before use, then it's not too much of a concern. If, for example, a person boosts the Ca++ in their salt mix by 40 ppm (if it's a lower Ca++ salt mix, for example) then they'll boots Br- by 1 ppm, which I don't think is anything to be concerned with. It's the longterm usage and hence potential build-up of high levels of Br- that we're concerned with.
CaCl2 products like those from Kent, ESV, Bulk Reef Supply, etc. are either from Dow but before the change in manufacturing process, or from some other source. Hence, elevated Br- is not a concern with any of these that we would normally consider using. That's what I was referring to above, albeit not as clearly as I should have.
For a one-time or very rare bump in Ca++, the new formula Dow is probably fine. For regular supplementation I'd track down one of the other sources that do not have elevated Br-.
Chris