The movement of water in the aquarium is probably a subject to which most of us give little direct thought. However, it is one of the vital functions in the aquarium and is directly responsible for a number of important processes.
Water movement can be achieved in several ways.
Consider an aquarium filled with water with perhaps, a gravel substrate and some rocks and plants. In such an environment, very little water movement takes place.
If we add a heater to our aquarium, water movement is generated by convection currents, as the warm water around the heater rises (warm water is lighter than cold water) and is replaced by colder water. With just the heater in the tank, however, we will end up with a layering effect, with the warm water sitting at the top of the tank and the cold at the bottom.
If we now add some fishes to the tank, a certain amount of water movement will be generated mechanically by their fins pushing against the water as they swim around. The amount of water movement generated in this way will depend upon the size and number of fishes in the tank. For example, if we only have half a dozen Neon Tetras in the tank, the amount of water movement will be negligible.
If we now add an air stone, or some other device which generates a stream of bubbles, such as a box filter, a much greater amount of water movement is generated mechanically by the air bubbles rising in the water.
If we wish to create an even greater amount of water movement in our aquarium, we can use a power filter, which will forcibly pump water around the tank, thereby generating very strong water movement.
So, now that we have discussed how to move water around the aquarium, let us look at some of the functions water movement performs.
Firstly, water movement will overcome the problem of thermal layering by mixing the warm and cold water layers, so we end up with an evenly heated tank.
The movement of water in the tank also prevents the formation of a film on the water surface, which would inhibit gaseous exchange between the water and the air.
Water moving around the tank effectively increases the surface area of the tank by constantly changing the layer of water in contact with the atmosphere. This, of course, dramatically increases the rate at which oxygen can be dissolved into the water and carbon dioxide released into the air. Well oxygenated water is essential for the health of the fishes, plus, we can keep more fishes in a given space if the water is well oxygenated.
Moving water carries oxygen to the nitrifying bacteria in the tank, which are responsible for the breakdown of harmful waste products, and also carries nutrients to the plants.
A strong movement of water in the aquarium, as produced by a power filter, provides the fishes with a current in which to swim, and many fishes find this both enjoyable and beneficial.
As you can see then, water movement in the aquarium can be tailored to suit the type of environment we wish to establish.