OXYGEN AND CARBON DIOXIDE LEVELS

OXYGEN AND CARBON DIOXIDE LEVELS

Oxygen is soluble in water, but not very well. Dissolved oxygen may range from 0 PPM. For keeping fish, concentrations of 8 PPM and a above are desirable.
The key to oxygenation is to increase surface contact of air and water. One common misconception is that the air bubbles of an air stone are adding oxygen to the water. They are, but only to the extent that on the way to the surface they push a column of tank water into contact with the air at the water’s surface. We can increase oxygenation just as effectively with a submersible water pump by resting the pump on the tank bottom and aiming the output at the surface. In this manner, you can generate tremendous exposure of water to air at the water surface and gas exchange.
Oxygen is very important to the nitrifying bacteria of the filter because oxygen is integral to the production of nitrite from ammonia. (See the discussion of ammonia above). Warm water carries less dissolved oxygen than cold water, a fact that is significant to the health of both your fish and your filter. As mentioned earlier in this book, keeping Arowana at high temperatures ( above eighty degrees ) increases the oxygen demand of the fish and filter bacteria, while at the same time warmer temperatures actually reduce the ability of the water to provide the much Eneeded oxygen. Cold water, on the other hand, carries a near Esaturation value of dissolved oxygen without much circulation or surface agitation at all. Why is this relevant? Because when considering certain water treatments that consume dissolved oxygen Esuch as potassium permanganate and formalin Eyou must remember that cold water is better than warm water.
The fact that cold water carries more oxygen also means that when fish are to be shipped or transported from one place to another, whether across oceans or to the local vet, water of a temperature less than seventy degrees is preferable.
In heavily planted aquariums, dissolved oxygen follows a daily cycle. By day, plants engage in photosynthesis and produce considerable amounts of dissolved oxygen. In some cases you can actually see tiny bubbles rising from the leaves. At night, the plants grow and respire. They reverse their metabolism and produce carbon dioxide and take in dissolved oxygen. The miniscule algae are no different from more complex plants in this regard. As a result, a heavily planted tank or a tank with a lot of suspended green algae may have low dissolved oxygen levels at night.
Carbon dioxide is produced by the respiration of both plants and animals. When you exhale, you produce carbon dioxide. Carbon dioxide levels can exist independently from the oxygen concentration in water. For example, water may have large amounts of oxygen and carbon dioxide at the same time.
In water, carbon dioxide readily converts to carbonic acid, which in turn tends to lower the pH. A large number of fish in a small tank with minimal circulation and surface agitation may actually accumulate sufficient carbon dioxide to lower the pH. On the other hand, removal of carbon dioxide by increasing surface exposure and gas exchange will remove the source of carbonic acid and may raise the pH.
Remedies to carbon dioxide accumulation include increasing surface exchange with air stones or pumps. As suggested earlier, raising the dissolved oxygen of the system does not decrease the carbon dioxide levels, but increasing surface exchange of air and water is a step toward maximizing both.