Food particles and other debris are also pulled down into the gravel. A water change also replaces essential trace elements that organisms have used. The pungent odor that lingers in the air following a lightning discharge is ozone gas. To form ozone, a considerable amount of energy in the form of electricity or ultra-violet radiation from the sun must come in contact with O 2 . The energy causes O 2 to form a bond with another oxygen atom, forming O 3 .
Ozone is very unstable and reacts readily with carbon compounds.
Ozone disinfects water through oxidation. By breaking the bonds which hold the elements of an organic compound together, ozone has the ability to destroy bacteria, fungi, viruses, and large organic molecules. Ozone has been used in this way for drinking water purification in Europe since l907. Compared to chlorine, another oxidizing agent, ozone has several benefits. For example, it does not combine with organic compounds in the water to form toxic substances called chloramines.