I know alot of people do it, but... I would only store CS in glass bottles.
Also, the light and dark prerequisite is based on whether you're storing ionic silver solutions. Whereas the particle or metallic variants can be stored in light without issue.
No clue on the magnesium chloride, though I take a daily dose of magnesium and often use Epson salt baths to deal with cramping etc. without any notable conflicts with Colloidal Silver . - I take cs 3 x p/day, every day.