Strontium supply for coral tanks
Strontium is no longer a bulk mineral in sea water, although it is also not particularly rare at about 8 mg/l. It has no function in animal or plant metabolism, but is used exclusively as a structural element. In this role, it is essential for the development of hard coral skeletons because it is embedded isomorphically (i.e. structural identic) into the structure of the crystal lattice of the aragonite* (modification of lime and the main component of the coralline limestone) and provides stability against the destructive remodelling into calcite.
Barium is also embedded in trace amounts in the aragonite* of the coralline limestone skeleton, where it has the same function as Strontium.
* If aragonite was not stabilised through foreign ions, it would rapidly transform into calcite and hence destroy the structure of coral skeletons, because it is a form of calcium carbonate which is only metastable under the conditions that prevail in seawater basins.