Sponge filters add oxygen to an aquarium by increasing the gas exchange that occurs at the water surface. This happens because the popping bubbles increase the total surface area between the water and atmosphere.
In this article you will discover how oxygen is absorbed into your aquarium.
How sponge filters increase an aquarium’s oxygen levels
Sponge filters do not increase an aquarium’s oxygen levels in the way you might think. A sponge filter’s bubble do not inject oxygen into the tank.
How oxygen is added to an aquarium
Oxygen dissolves into a body of water when it comes into contact with the atmosphere. Oxygen is also produced by aquatic plants and algae as a byproduct of photosynthesis. Plants convert carbon dioxide and respire oxygen into the water column.
Sponge filters add air bubbles into the water
A sponge filter is powered by an air stone. What happens is a pump pushes air through airline tubing and forces it through an stone with a bunch of tiny holes.
This air stone is placed inside of the sponge filter in an aquarium. The result is a bunch of small air bubbles that originate from inside the center of the sponge filter.
Air bubbles create surface agitation and increase surface area
These air bubbles rise to the top of the tank and pop, creating turbulance on an otherwise stagnant water surface. This turbulance increases the total surface area between the water and the atmosphere.
It is this increase in surface area that allows the process of oxygen absorption to happen more quickly. More contact between the air and the water means more oxygen dissolves into the aquarium water.
How much oxygen do sponge filters add?
The most accurate method for measuring dissolved oxygen is by using optical or electochemical sensors, which usually cost between $300-$600. There are no practical oxygen sensors or test kits available for aquarists like there are for other water parameters.
However, knowing that oxygen absorption is due to an aquarium’s surface area, you can get a fairly good visual sense of the difference by simply observing the ripples on your aquarium’s surface.