How much flakes in a bath tub?

Let's do a small exercise about dissolving MgCl2 flakes. First thing to know is that the best effects are reported by users who dissolve 3 – 5% concentration in their bath tub. (Concentration by weight)

Taking into account the conic shape; position of the overflow and water displacement by body volume, on average there’s about 65 liters of water in the bath tub.
65 Liters of water equals roughly 65 kg of water. In order to have a > (greater than) 3% concentration of MgCl2 by weight, one should add:
> 65 x 0.03 =
> 1.95 kg pure MgCl2
By nature MgCl2 –flakes contain 47% pure MgCl2 and 63% crystal water.

> 1.95 kg pure MgCl2 equals
> 1.95 / 47 x 100 =
> 4.14 kg Flakes.

The Magnesium Health Institute recommends 4 – 5 kg of MgCl2 – flakes in an 'average' bath tub for the best effect.

'DIY magnesium oil' ?

Question: can I make magnesium oil from magnesium flakes?
Answer: yes, however, don't use 'do-it-yourself magnesium oil'!


Magnesium oil
Magnesium oil is not actually oil but is referred to as such because it feels so smooth. It is actually the highest concentrated liquid form of pure natural magnesium chloride, dissolved in water (brine):

MgCl2 31%, density 1310 gr/l

Natural magnesium oil meets  all topical demands, assuming that it is produced under a strict regime and controlled continuously with regard to composition, and trace elements, etc.

1,000 g magnesium oil contains 690 g water (69%)


Magnesium flakes
Magnesium chloride flakes are crystallized magnesium  chloride. Actually it is an hexahydrate: each molecule  MgCl2 is surrounded by 6 molecules of crystal -       water: MgCl2(H2O)6

MgCl2 47%, density 1569 gr/l

Flakes are produced by an evaporating process.  

Magnesium oil (the brine) is heated up to approximately    1600 Celsius; water is evaporated and  MgCl2 flakes  remain    after crystallization on a cooling-belt.
1,000 g MgCl2 flakes holds 530 g(crystal-)water  (53%)

Unpredictable chemical reactions
When using redissolved magnesium chloride flakes in high concentrations unpredictable chemical reactions may occur.

Many (re-)dissolving tests were performed
Due to heating for evaporation, magnesium chloride flakes come with very small amounts of by-products like MgOHCl (magnesium hydroxide chloride) and MgCO3 (magnesium carbonate). This explains the white haze that might occur after dissolving flakes. It is completely negligible for applications up to 5% (e.g. bath or foot soak)

In addition, there are always minor amounts of trace elements which are completely unharmful under normal conditions or even required as life essentials. But  they react to an increasing extent unpredictably when flakes are dissolved in increasingly higher concentrations. Together with everyday ingredients, such as oxygen, there is always the risk that undesirable or even harmful by-products occur.


  • Flakes may not be used in a concentration higher than 5% (e.g. bath or foot soak)
  • The purest  MgCl2 is indispensable for topical applications (concentration up to 31% )
  • The Magnesium Health Institute strongly discommends  ‘DIY  magnesium oil’ 

What is Magnesium Oil?

Magnesium oil is not actually oil but is referred to as such because it feels so smooth. It is actually the highest concentrated liquid form of pure natural magnesium chloride, dissolved in water.

How much magnesium equals 5 ml of Magnesium Oil?

5 ml of Magnesium Oil (MgCl2 31%, density 1310 gr/l)
6,6 g MagOil (or liquid/brine)

1 g Magoil
77 mg elemental Mg

5 ml of Magnesium Oil
6,6 x 77 =
508 mg of elemental Magnesium

Does drugs deplete magnesium in the body?

Hundreds of drugs cause magnesium deficiency. See this document for a list of drugs that has influence on magnesium in the body:

Question: A client wrote to me, stating that his blood magnesium levels were tested several times and were always considered fine.

Still, as he recognised symptoms of a magnesium deficiency, he decided to investigate the magnesium levels in his urine. Those tests showed that large amounts of magnesium were excreted through urination.
The treating doctor called it a renal leak and that was the end of the matter: kidneys excrete magnesium. Is my reasoning correct that, in this case, transdermal absorption would be a solution? Are the kidneys bypassed in this manner, and is the magnesium directly absorbed into the blood?

Answer: An interesting question, but the matter is a bit more complicated…..

First of all, magnesium loss through the kidneys is probably much more common than the frequency with which it is currently diagnosed would suggest. This has to do with the fact that, to determine the magnesium status, we are still dependent on measuring the serum magnesium: the levels of magnesium in the blood.

However, our blood only contains about 1% of the total body magnesium. Moreover, our blood tends to keep the serum magnesium as constant as possible. Even at the expense of the so-called free magnesium in the interstitium, the space around the cells. By the time we measure reduced blood- or serum values, the patient is always already in an advanced state of hypomagnesaemia.

Apparently, the person involved suffers from renal hypomagnesaemia, which is an increased excretion of magnesium through the kidneys. This can be caused by various causes, such as certain medicines, kidney damage, or genetic disorders. This often involves a disturbance in the reuptake of magnesium from the pre-urine before it is excreted as urine.

Extra supplementation, therefore, is of great importance. If you were to only supplement orally with, for example, magnesium citrate, which has a good bioavailability profile, the amount you would need could lead to intestinal problems. This could result in diarrhea and because of that have the adverse effect of losing additional magnesium through intestinal excretion.

The idea of using transdermal supplementation, in addition to oral supplementation, is understandable. A transdermal route is less stressful for the the intestines, after all.

However, the uptake mechanism of magnesium absorption through the skin is similar to the reabsorption process of magnesium in the kidneys. We know that for certain genetic causes of renal magnesium loss, the transdermal route can also be compromised.