IN DEFENSE OF THE AIR PUMP
by Antonios T. Andronoglou
THIS ARTICLE APPEARED IN THE SEPTEMBER 2002 ISSUE OF FAMA
Don’t dump the Air Pump!
As I will try to explain, the Air Pump is a very important piece of equipment for a number of reasons and it should not be considered obsolete. We just need to understand all aspects of its use, which might not be obvious at first.
Water AND Air.
We will all agree that fish need water and air. In order to achieve this, we strive to provide clean and healthy water using various filtration techniques and water changes, and also circulate the water using water pumps or air bubblers.
Circulation brings water near the surface where it can react with ambient air achieving gas exchange. This means that water must absorb Oxygen from the air, at the same time releasing Carbon Dioxide to the air. There is not much difference in the method used to circulate the water, as long as it is done in a fashion that pleases the eye and is not disturbing to the fish and other inhabitants of the aquarium.
When water comes to the surface to react with air and achieve gas exchange, it must meet clean air, rich in Oxygen and absorb as much as possible, at the same time releasing as much Carbon Dioxide as possible to that air.
It all looks all right so far. Now lets think about some elementary physics. We know that Carbon Dioxide is heavier than Oxygen. So, Carbon Dioxide stays near the bottom of any given container. That container could be a soda bottle, a cave, a basement, or the top of your aquarium.
It is true that many tanks have a tight fitting lid to prevent fish from jumping, to reduce evaporation, and even to prevent hands or objects from getting in the tank. The lid or hood, if lights are present as well, does not leave much room for air in that enclosed space. So after a while (a short or a long while) you have a layer of Carbon Dioxide next to the surface of the water. Is this good for gas exchange? NO. It actually defeats the purpose of gas exchange, unless you want to cut back on the use of that Carbon Dioxide dosing system!
This Carbon Dioxide layer can be blown off the water surface by vigorous surface water motion. It will also very slowly diffuse through the openings of the tank lid. And the air from bursting air bubbles can displace it. From the above methods, displacement is the safest, and more easily accomplished one. But we need to think about what we are displacing the Carbon Dioxide with. If we use water pumps in the aquarium then the venturi feature (if used at all) usually draws air from under the lid or hood. This is not the best place to draw air from, due to its high Carbon Dioxide content. But an Air Pump will almost always draw air from outside the hood, bringing better quality air in regard to Carbon Dioxide content to the water surface.
Maximum Air Motion.
Even a medium sized Air Pump will create bubbles of air volume exceeding many times that of venturi water pumps. The effect of this is that it creates air turbulence and displacement of the stagnant and polluted air over the water surface.
Now lets think about where the Air Pump is located and draws air from. We usually put it in the tank cabinet, or maybe on a shelve over the tank if we followed the Air Pump’s manufacturer directions and placed it above the waterline.
This means that we draw room air. Is this good enough? If the air in the room is polluted from smoke, odors etc, then we could locate the Air Pump outside the room, or house and draw outside air. This is the best situation by far, because then we are using the freshest air for gas exchange. This can only be achieved with an Air Pump, no venturi water pump can do it! Even in hi-tech situations, a modest Air Pump can offer its services. I have used Air Pumps to bring fresh air in trickle filters, in venturi skimmers, even in needle wheel skimmers.
I understand that some people find air bubbles unsightly. I cannot argue with that. However if air bubbles are out of the question in a given tank, then displacement of the air above the water surface must be considered, because the water pump cannot do much over the surface, especially in tanks covered with a lid or hood.
Watch that Carbon Dioxide!
Sometimes the symptoms of Carbon Dioxide accumulating near the surface may go unnoticed or be interpreted as something else being the problem.
If Carbon Dioxide stays near the water surface, then the PH may drop suddenly at night, the fish may experience breathing difficulties, and even unexplained deaths can occur. It is easy to misinterpret all of the above, but if you do not bring fresh air to your tank, then this may be the cause of it.
Some will argue that the Oxygen content of water is that much smaller than the Oxygen content of air, and so it will take a long time to use up all the Oxygen of the stagnant air over the surface. Maybe it is so, but combine the fact that Carbon Dioxide is heavier that Oxygen and so it stays near the water surface, the fact that Carbon Dioxide lowers PH, the fact that PH drops at night and then if you think like me, you would prefer to be safe than sorry!
Keep the Air pumping!
Consider this analogy. Say you are in a room with closed doors and windows, but you have lots of air circulation and air conditioning. You wouldn’t want to wait until all the Oxygen in the room is depleted to open a window to get fresh air.
The fish cannot talk to you to ask for fresh air. They will get sick from stress or die instead. The situation gets more dangerous at night when everything alive respires Carbon Dioxide. A simple inexpensive and indispensable device can solve this. An air bubbler or even a free outlet from a small Air Pump over the water surface, if you object to the sight of bubbles, will suffice.
So, if a stream of bubbles does not define an aquarium for you, think again about what happens above the water surface, and if you decide to go without an Air Pump, then devise a way to deal with Carbon Dioxide accumulation in that layer of stagnant air near the surface.
For all others, the traditional air bubbler will give us peace of mind!
You can contact the author at firstname.lastname@example.org