Calcification is the creation, use of, or deposition of calcium carbonate (CaCo3) by a living organism, or through chemical processes.
As a point of reference, calcification is the process involved in the growth and creation of bones, teeth, and fingernails, and the method used by hard corals to create their complex structures.
Calcification is sometimes seen in an aquarium when algae or plants cannot obtain enough carbon from low levels of carbon dioxide (CO2) and instead they take carbon from minerals in the water, leaving behind deposits of calcium carbonate.
Calcification on plants can sometimes be seen as a chalky deposit on the leaves and is particularly common on hard water plants like vallisneria. Sometimes the process is referred to as 'biogenic decalcification'.