Magnesium metal

Cory · Jul 24, 2018

Im curious, could we add high purity magnesium metal to our ro/di water to dose magnesium?

I watched a video that shows magnesium forms magnesium hydroxide when put into water. So i was curious if this could be used to boost magnesium and alkalinity at the same time? Magnesium metal seems much cheaper than high purity magnesium chloride.

sghera64 · Jul 25, 2018

Cory said:
Im curious, could we add high purity magnesium metal to our ro/di water to dose magnesium?

I watched a video that shows magnesium forms magnesium hydroxide when put into water. So i was curious if this could be used to boost magnesium and alkalinity at the same time? Magnesium metal seems much cheaper than high purity magnesium chloride.

Pulling from my materials class (some 35 years ago), I believe the oxide would form a protective “skin” on the magnesium metal. It would not slough off and the rest of the metal inside would be protected from further “corrosion”.

Now, if you used Mg ribbon or chips and tumbled them around so that they scrape against each other, you might knock off some of that “skin”. I’m not sure what that Mg(OH)2 matrix looks like. It might not be individual Mg(OH)2 molecules, but more of an amorphous solid - - not very useful in a reef. Mg(OH)2 has very low solubility in pure water. So, it would dissolve, but very, very slowly.

When we dissolve MgSO4 or Mg(Cl)2 into water we get a bunch of Mg++ ions. Adding that to our higher pH tanks (loaded with bicarbonate, carbonate and -OH), I’m sure we get some Mg(OH)2 and MgCO3 which are limited in their water solubility - but they are added as ions into a saltwater
matrix that can help keep it soluble.

Maybe Randy Holmes-Farley can give a better explanation.

Cory · Jul 28, 2018

Randy Holmes-Farley · Jul 29, 2018

Magnesium hydroxide is far, far less soluble in water than is calcium hydroxide (kalkwasser). It would be nearly useless in RO/DI, but if you really wanted to do it, I'd get USP magnesium hydroxide like this:

https://www.etsy.com/listing/575547...MIyquTwNHE3AIV2YuzCh0JWwlZEAQYAyABEgJwKfD_BwE