I'll chime in too and say that Colin's customer service is outstanding. I've bought several things from him and have had many questions, all of which he was happy to answer and in a VERY timely manner.
To prevent mold, it was recommended to me by another forum member to mix in this order - Fill container partially with distilled or RODI water, then add 5ml of vinegar into the distilled water, shake that up and then add your dry packet to the water and shake vigorously, then let sit overnight. You could add another step at the beginning - sterilizing the container with bleach or by boiling.
I agree that this does look more like precipitate, though.