If the body only absorbs what it needs why do people get Mg toxicity from sea water?

I have been trying to counter this I also get itchy skin sometimes. It does not happen if you wash off your skin after a few hours.
I found out the reason so I thought I would share it with you.
Our skin PH is ideally 4.6 to 6 The lesser the better. As good bacteria survive in slightly acidic PH
Our skin has trillions of good bacteria that save our skin from thousands of bad bacteria that are flesh eating(yeah thats what happens when you die bacteria eat your flesh because the PH value goes up/alkaline).
You know those itchy rashes and microscopic cuts when you get infection in your groin is caused by ammonia produces by bad bacteria.
So that is why your skin literally tears with the ammonia produced while good bacteriar produce acids like lactic acid and acetic acid that is why they cant survive in alkaline ammonia while bad bacteria cannot survie in acids. That is why your curd, saurkraut does not get spoiled once the good bacteria take over and start producing acids.
So magnesium is alkaline. The Ph value of magnesium varies from 2-3 to even 8
So its hard to say which one or I have not found information on which kind of Magnesium is highly alkaline. I know that magnesium sulphate is highly alkaline and it can actually crack your skin.
So now What I do is wash off the magensium chloride after sometime.
This happens more as you magensium levels return to normal.
I am looking at adding apple cider vinegar to Magnesium oil/water to decrease the PH
But not sure if it would help. Trying to find some information online.
I am also looking to adding MGcl in Coconut oil and see how it works. If it is less irritating.
I am also thinking of adding MSM as I heard it raises acidity.
Overall the skin is getting alkaline which is not good Either wash it off it may help or wash with lactic acid and or ACV to restore the PH of the skin