The use of Airstones and Bubblers

(by  JohnK)

While it is true that a gas can only dissolve in a liquid at a surface, airstones and bubblers do, in fact, increase surface area of the liquid. A bubble is a spherical air/liquid surface. Multiple bubbles serve to increase the total surface area of the liquid. It is at this air/liquid interface that the dissolution of the gas into the liquid occurs. Not only do they increase the surface area while below the main surface of the water, they also increase the surface area at the main surface as they create little hemispheres of water poking up above the main surface.

As empirical evidence, consider the well-documented phenomenon of CO2 bubblers in fish tanks. In order to keep from choking the fish, yet still provide sufficient CO2 for plants, they must provide bubble-counters to limit the number of bubbles of CO2 released into the tank. Why else control these bubbles if they do not increase the dissolution of the gas into the liquid?

Another well-documented situation is that of the homebrewer who force-carbonates his beer. It has been repeatedly shown that attaching a stainless airstone (so it can be sterlized) to the bottom of the CO2 intake tube, extending down into the uncarbonated beer, then forcing the CO2 through the airstone and up through the beer in the form of bubbles decreases the time it takes to fully carbonate the beer when compared to simply forcing a blanket of CO2 on top of the beer, then agitating.

The question then becomes, not "do airstones increase the Oxygen content of the water" to "is the increase in Oxygen caused by airstones required for proper fish maintenance?" From what I've read here and elsewhere, probably not. There is sufficient agitation and water/oxygen interface present in a properly setup aquarium to provide for the fish without having to add airstones. If, however, you are having problems that seem to be related to insufficient oxygen in your tank, you might want to consider adding an airstone or two and measure the difference.


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