Will an airpump increase the CO2 level in my aquarium?

Question

Air pumps (let's say with 200 l/h) slightly increase the level of oxygen in the water simply by making bubbles rise from the bottom of the aquarium to the water surface. Can I expect an (even minimal) effect for the CO₂ level as well?

I know that concentrated CO₂ from a bio facility or a bottle is disolved using a flipper or a diffusor and that's the way to go for reliable CO₂ supply (otherwise there'd be no CO₂ facilities for aquariums), but since pumping masses of air and therefore increasing the level in the water has an effect for the gas O₂ it might have one for the gas CO₂ as well.

I have a 60 l freshwater aquarium with 35 cm distance between the gravel surface and the water surface.

Answer 1

No, aeration will typically cause CO₂ degassing unless the room the tank is in has substantially elevated CO₂ levels. I've personally tested the differences in CO₂ concentration when aerating and not aerating, with other factors controlled, and CO₂ levels go down or have negligible change, likely depending on the initial concentration.

I do not know the specific chemical mechanism for this, but I suspect that O₂ is far more solvent in water so the increased surface area is consumed by O₂ absorption rather than CO₂ absorption. The increased surface area due to aeration is the primary mechanism for this as far as what I've read. Additionally, CO₂ levels remain fairly consistent due to surface tension, again with aeration, that surface tension is broken, allowing CO₂ to degas. If I can find a specific reference to this phenomenon, I will update this post. But at least anecdotally in several decades of keeping planted tanks, aeration and increased surface area through mechanical means, decreases CO₂ concentration and increases O₂ absorption.

Answer 2

CO₂ is far more soluble in water than O₂. The problem is the amount of CO₂ in air. Air is only about 0.0407% CO₂. There is just not enough of it. Dissolved gases compete with each other so even though CO₂ is more soluble it does not compete for space with O₂ and N₂ that dominate air.

That said the ocean has a lot of CO₂ but there is a lot of ocean.

Answer 3

Maybe, depends on how many vigorous plants you have. If you have no plants it will make little difference. Many growing plants will be absorbing CO₂ from the water and so the water will have less than equilibrium level of CO₂ relative to the air, and an aerator will add CO₂. I had a 75 g salt tank with a lot of Caulerpa (algae) in it - I sold it to pet shops to get rid of it. At night the pH would get more acidic because of the increased CO₂ saturation (down to about 8.2) with aerators running. During the day the plants consumed so much CO₂ that the filtering and aeration could not replace it fast enough and the pH went to about 8.7. The numbers don't sound like much, but consider that is changing the pH of about 700 lbs of water. Too hard for me to calculate how many pounds of CO₂ that required.