You can place dead coral in a freshwater aquarium, but it will increase the hardness and pH level of the water. However, if the pH level of the water in your aquarium is low, you can add dead corals to the aquarium to increase it. The primary component of coral is calcium carbonate (CaCO3), the same element that is found in limestone. Polyps, one of the main constituents of coral, are classified as invertebrates. They pump out limestone, which can be found on the skeletal remains of other types of polyps. Polyps spend the day hiding and protecting themselves inside their homes, and they eat at night. Corals are incapable of producing their own nutrition. When dead coral is exposed to water, they produce a compound known as calcium bicarbonate as a result of a chemical reaction with its own properties. We can find this compound in freshwater in the form of calcium ions, bicarbonate ions, and carbonate ions. Corals, when placed in fish tanks, the freshwater in the tanks become more mineralized because of the calcium ions that are formed as a byproduct of the corals’ decomposition.