Magnesium is present in NSW in a fairly high concentration (1300 - 1400mg/L).

It is the third most abundant element in seawater and it is used in various kind of biological processes such as photosynthesis, calcification, and homeostasis.

Magnesium also prevents the precipitation of calcium from saltwater.

Maintaining a correct magnesium concentration is very important and is indirectly responsible for fast coral and calcareous algae growth by virtue of making the maintenance of correct calcium and alkalinity figures possible.

Magnesium is depleted by algae, the excessive use of  kalkwasser and by going far beyond natural calcium, alkalinity and pH values.