• Oxygenation or Aeration in fish tanks

We mentioned earlier that the water you use for your aquarium needs to be oxygenated. This just means that there is a certain minimum amount of oxygen gas dissolved in the water. There's no magic trick to this. Water that is exposed to air will absorb oxygen until it reaches an equilibrium level determined by factors such as atmospheric pressure, temperature and dissolved solids. So all that's needed is that the water you use is exposed to air for a certain period of time before you add it to your aquarium. If you draw water from a tap into a bucket, mix it with dechlorinator, and pour it into your aquarium, that should be sufficient to oxygenate the water. You may find, if your water comes from a well or from a closed container of some type, that it lacks sufficient dissolved oxygen to support aquatic life. In this case, you should leave the water in an open container and perhaps agitate it with an air pump or powerhead for at least 15 minutes. Then it should be safe to add to your aquarium.

A more common term that is used by aquarists is aeration. Aeration and oxygenation really mean the same thing. They both mean adding dissolved oxygen to water. When live fish, plants, and bacteria are in an aquarium, they are constantly consuming the dissolved oxygen. (When the lights are on, plants both produce and consume oxygen.) So to insure that the oxygen supply does not run out, the tank water must be aerated. In it's simplest form, aeration is accomplished by circulating the water so that the water at the bottom is moved up to the surface where it comes into contact with the air and absorbs oxygen. If circulation is sufficient, the amount of oxygen that dissolves into the water will exceed the amount that the fish are consuming and everything will work fine. If there is insufficient oxygen, the fish will either come to the surface and gasp for air, or they will become sluggish and ventilate (move their gills and mouths) rapidly. It extreme cases, the fish will begin to die. The same is true for the ammonia-eating bacteria that are needed to remove wastes. You won't see them dying, but ammonia will build up in the tank and hasten the death of your fishes.

Most filter systems will help with aerating the aquarium water by circulating it. Some have a venturi feature that draws air into the out-flow of the filter and brings it into contact with the water. Many powerheads have a venturi feature which is very effective at aerating the water. Filters that are powered by an air pump are constantly aiding aeration by pumping bubbles through the water column. The bubbles themselves are not small enough to dissolve into the water, but the air in the bubbles will dissolve into the water as the bubbles rise. At the same time, the stream of bubbles also pushes water up toward the surface where more oxygen can be absorbed. Air pumps and powerheads can be used apart from filter systems to increase the aeration of your aquarium. Air pumps alone are usually used with some type of airstone or diffuser to create many tiny bubbles.

When deciding what type of aeration you need, several factors should be considered. First of all, warm water will hold less oxygen than cool water. And salty water will hold less oxygen than freshwater. As nitrate and other wastes build up in the tank, the oxygen capacity of the water decreases. So, again, water changes are important for keeping your fish in good health.

Some fishes require a higher dissolved oxygen concentration than do others. In fact some fishes can actually breathe air from the surface of the water and live in very low-oxygen waters. These include gouramis, bettas, bowfin and Corydoras and Hoplosternum catfishes. Other fishes need extra oxygen. Fishes that come from cool, flowing waters or that are highly active swimmers, often need more oxygen than others. Seek advice from knowledgeable sources about the needs of your fishes.

Of course the most obvious factor to consider regarding aeration is the number and size of fish in the tank. The more fish, and the larger they are, the more oxygen that is needed. Avoid crowding the fish, and normal aeration measures will be sufficient.