Airstones provide life-esential oxygen to the fish and invertebrates in the water by keeping the surface of the water in constant motion. The action of airstones brings new water to the surface (air/water interface) in which the oxygen in the air can enter and from which harmful gases such as carbon dioxide can be disipated. It is important to note that it is at the surface, where the water is brought in contact with the air, that most dissolving of oxygen into the water occurs.
The concentration of available oxygen in water is extremely critical because there is so little of it in liquids. Air consists of over 20% oxygen, or 200,000 parts per million. Water is, however, entirely different. Normally water has only about 0.0006% or 6 ppm-which is 1/33,333 the oxygen supply in air! This means that fish and other "water-breathing" aquatic animals have had to evolve super efficient mechanisms for getting oxygen out of the water. They usually need a minimum of 4 ppm oxygen for good health, and preferably an optimum over 6 ppm. The conditions are even more rigorous for marine animals, because salt water may hold 2 ppm less oxygen than fresh water of the same temperature. The greater the amount of dissolved salts in the water, the less oxygen it will hold. To make the situation more complicated, the higher the temperature of the water, the less oxygen it can hold. There is about a 1 ppm difference in the amount of oxygen that can be in water at 70° F (21° C) and 86° F (30° C).
Airstones provide even temperatures throughout the aquarium preventing the development of thermoclines by keeping the water constantly mixing. Thermoclines are stratifications of waters into layers with a different temperature in each layer. In addition, during the night aquatic plants take in oxygen in their respiration and give off carbon dioxide. Under certain circumstances the removal of too much oxygen can cause the suffocation of aquarium animals such as fish. Airstones working constantly keep oxygen coming into the water and harmful carbon dioxide dispersing out of the water, maintaining the aquarium water in proper balance.
There are other facts that show how important good aeration is for the proper functioning of aquariums. As mentioned previously, carbon dioxide is removed from the water into the air relatively easily with the vigorous use of airstones. However, the passage of oxygen from the air into the water is much slower; it may take two hours or more to replenish sufficient oxygen into the aquarium water that has a greatly depleted oxygen level.
Another way in which oxygen can be dangerously exhausted is by stirring up the mulm and other bottom debris in old established aquariums. There are large numbers of bacteria in bottom materials, and their renewed activity after gaining access to new food materials and oxygen can greatly lower the oxygen level in the water. Aeration and high levels of oxygen are vital in the process of biological filtration. Aerobic bacteria (bacteria requiring oxygen) in the biological nitrogen cycle require substantial amounts of oxygen and will cease to function below 1 ppm oxygen level in the water. Should a chronic decrease of oxygen occur, aerobic bacterial activity will be replaced by anerobic bacteria (bacteria not requiring oxygen). These bacteria are harmful and will produce toxic products dangerous to aquatic animals. The proper functioning of the biological filter bacteria will thus be impaired.
In addition to regular aeration techniques there are other products to aid fish temporarily from becoming asphyxiated. Oxygen can be quickly and safely added short term to the water in an emergency by using hydrogen peroxide from the drug store. Fish which have been transported long distances and suffer from nitrite poisoning and methhemoglobin problems (oxygen-deprived hemoglobin in the blood) can be treated with KORDON METHYLENE BLUE.