CaCO3

From The Aquarium Wiki

Calcium carbonate (CaCO3)

Calcium carbonate is a chemical compound. It is commonly used medically as a calcium supplement or as an antacid. It is also a common substance found as rock (like marble) in all parts of the world and so is often found in nature dissolved in water which flows over these rocks. It is therefore the principle cause of hard water.

CaCO3 is the main building block of seashells and the shell of snails and all shrimps.

This compound is sold over the counters at shops for health, cooking or for hardening water for swimming pools.

It is used in aquariums as a principle method to increase the general hardness (GH) of the water. Many plants, aquatic species require a level of hardness in the water to buld their bones and external body parts. For example aquatic snails need a GH of at least 10d to stop their outer casing from dissolving into the water and killing the animal.

See the GH page for more on 'General Hardness'.