Transdermal Magnesium Chloride - How Much?

Hello,

I have this bottle of Magnesium Chloride here.
The label says it contains only water and magnesium chloride.
It doesn't say how much of each.

I understand that you can spray this directly on your skin and let ir absorb through the skin.

However, when I do this, my skin gets itchy and a bit red. (goes away)
Is it supposed to itch? Should I dilute with something first?

Also, how much should I use every day?
I currently supplement with 800mg magnesium l-aspartate daily.
How much would I need to spray on my skin to get a roughly similar magnesium level in my body?

The brand of the magnesium chloride oil I have here is "Ancient Minerals" from Holland, if that helps.