Reef Status: Magnesium Carbonate & Borate

Natural seawater concentration for magnesium is approximately 1,300 mg/L. The magnesium concentration in kalkwasser treated aquaria may be as low as 600 – 700 mg/L. In general, it is prudent to maintain magnesium concentrations in reef aquaria between 1,200–1,400 mg/L.

Natural seawater has a total alkalinity of about 2.5 meq/L, of which about 0.1 – 0.2 meq/L is from borate. In an aquarium, it is advantageous for both pH control and improved calcium stability to have a higher borate content. This, however, should not be at the expense of carbonate. It is useful, then, to maintain a total alkalinity of about 4 – 5 meq/L with a borate component of about 1.5 – 2.0 meq/L.