For those interested
Ok, heard back from Chris already, and as I hoped and expected, it is nothing to worry about, just a bit annoying. Here is his response:
"Hello Dave,
Thank you. Indeed, what you are seeing are the insoluble particles I referred to in my previous e-mail. The abundance in the pail appears to be higher than one would normally see, and this is likely a result of variation in the anhydrous magnesium chloride that is used. The particles are completely inert; they are oxides of magnesium that form during the production process of that material. There is no reason not to use the resultant water that has been prepared.
Rather than use anhydrous magnesium salts, many manufacturers choose to use hydrated magnesium salts, which contain ammonia and heavy metals in many cases (depending upon the grade utilized). We prefer to go with the lesser of two evils, even though the anhydrous material costs an order of magnitude more than the hydrated material. I apologize for the appearance of these particles in the salt; we do our best to limit their prevalence but unfortunately its a natural aspect of the material itself that we have limited control over. Even if some of the particles were to enter the system, they would have no negative impact on anything.
Kindest regards,
Chris"
