Firstly what does an aquarium air pump actually do? Air pumps in aquariums pump air from outside the tank to the inside of a tank through an air outlet/s. This oxygenates your aquarium water by generally moving the surface water which produces more oxygen in your tank's water. Basically, the more surface water movement you have means the more the tank's water has contact with air. This process creates more oxygen in the water. The bubbles themselves actually do little to add oxygen to your water. However, they can produce beautiful effects.