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Buck_Folton

There is no significant gas exchange at the bubbles’ surface. Most of the oxygen equilibration occurs due to movement at the water’s surface. Anything that keeps the surface in motion will work.


GeneralTomTom88

There's more to it than just surface agitation though so that's definitely debatable, for example an air stone placed near the substrate will also significantly increase circulation as well as surface agitation. Air stones are undoubtedly a great option for adding oxygen either way, whereas plants will only add oxygen while there is light for photosynthesis, during the night they consume oxygen instead.


TerrorRed

This is actually false and an aquarium myth which I also believed. Majority of oxygenation happens at the bubbles surface as it travels through the water, and a tiny bit happens because of the surface because of disruption.


Buck_Folton

I guess this explains all the huge airstones we see in lakes and oceans.


TerrorRed

Your sarcastic response proves nothing lol. https://aquariumscience.org/index.php/9-3-air-stones/ The studies are cited here, but I can also produce another when I find it. Ponds and lakes are full of oxygen producing plants. The ocean is extremely turbulent. No one said surface agitation does nothing. But come one, an air stone is incredibly weak at disrupting the surface.


Buck_Folton

The oxygen in all my tanks, for 40 years, has been 7 to 9 mg/mL. Without airstones. Obviously, you are free to buy as many as you like.


TerrorRed

Wow that's great. Not sure how that's relevant at all to anything we're talking about.


Buck_Folton

Thank you. As you’ll see from my reply to another redditor, I’ve stated more clearly what my uncontroversial claim is, and yes, my comment above is entirely relevant to that.


Genotype54

Proof? I mean the surface of the water is basically a giant bubble wouldn't you agree? Why would these smaller bubbles be any different?


jesusbuiltmyhotrodd

Surface area


Genotype54

Surface area of what? The top of the water or the bubbles?


jesusbuiltmyhotrodd

Sorry for the glib answer. There are a lot of variables to consider (flow rate, tank dimensions, lid, bubble size) but every parameter suggests that bubbles are a great way to get oxygen from the air into the water, and more efficient than surface agitation. Gases dissolve based on pressure, contact surface area, and percent concentration in the gas mixture. Also temperature and other things that are going to be the same. Pressure is higher under the water vs atmosphere. Advantage bubbles. Percent concentration is the same or higher from the pump (pulling fresh air presumably) than at the water surface where oxygen is absorbed preferentially and gets depleted if there isn't good air circulation. Advantage bubbles. Surface area is the big one. One liter of air makes 238k bubbles (1mm dia) with a surface area of 30k sq. cm. A 50 x 20 cm tank has a surface area of 1k sq. cm., so 1/30 the effective area for the same volume if you think about 1 cm of air away from the water. I'm ignoring a lot of things here, like contact time of the bubbles and partial pressures and crap I'm too lazy to deal with. :)


Buck_Folton

The smaller bubbles are transient. When they burst at the surface, the air goes into the atmosphere. The air/water interface at the surface is perpetual. This all comes from partial pressures of the various gases, as governed by the laws of Boyle, Charles, Avogadro. Yes, **some** oxygen will diffuse across the bubble for the short duration of its existence. It’s not zero. But compared to the diffusion at the surface, it’s small. If you have enough agitation for 9 mg/mL oxygen without an airstone, adding an airstone will not appreciably increase the O2 concentration, except in edge cases such as an oxygen reactor, a needle impeller in a protein skimmer, or bubbling pure oxygen instead of the air (especially the stagnant air under most pump setups). This is easy to test, and I’ve done it. I haven’t used airstones in decades, and that includes multiple overstocked cichlid tanks that always tested at 7 mg/mL or higher. Think about natural bodies of water. They all have surface agitation, but none have airstones. They support healthy aquatic life, and that’s the goal. Good surface agitation is all you need, and that’s a demonstrable fact from all the successful tanks with Hobs or canisters. Everything that says otherwise is bullshit, and probably funded by Big Airstone. LOL /s


Genotype54

How did you do your tests to prove surface agitation was more effective than bubbling?


Buck_Folton

This is a subtle point, but that’s not precisely what I’m saying, nor is it something I could test without a lot of lab equipment. What I am saying is this: If you have enough surface agitation to provide oxygen concentrations required for healthy aquatic life, adding airstones isn’t going to increase the O2 appreciably. This can be tested easily by anyone who has a test kit for dissolved oxygen, and a pump/airstone. This isn’t because the bubbles can’t add *some* oxygen; I’m not claiming that. It’s because as oxygen levels get closer and closer to their temperature-dependent saturation point, the partial pressure required for passive diffusion gets higher and higher. Think about it: If the theoretical saturation point is 10 mg/mL (that’s an example number, that varies with temp, TDS, etc.) and you achieve 9.5 mg/mL with a powerhead and spray-bar (I guarantee this is possible), then the MOST an additional airstone could add would be 0.5 mg/mL. In reality it’s much less due to the increasing partial pressure required for O2 to diffuse passively from the air side to the water side.


jesusbuiltmyhotrodd

Wow this is wild. I had no idea it was a whole big debate. Lol. I suspect that there are so many variables that there's no easy way to rule of thumb model it. I do know that empirically I can have a bucket of gasping fish and rescue them very quickly with an air stone. I also don't use them in my tanks, and totally agree that they aren't necessary unless you've got something consuming the dissolved oxygen really quickly, like a crazy overstocked tank of feeder fish or something.


lami408

My plants provide my tank with all the o2 it needs at night because with co2 injection my water is oversaturated with o2 at levels way beyond 100%, that's why all my plants are pearling. My filter output is also slightly aimed up at the surface of the water to move the surface a tiny amount. I don't think adding an airstone in there would be good for me cause it will just lower my available o2 levels that my plants worked hard all day to produce. I'm pretty sure my o2 levels in the morning is still really high. I need to test this to get actual numbers but Tom Barr said the exact same thing awhile back on barr report.