# Do AIR BUBBLES dissolve oxygen into the water? Besides surface agitation



## Darkblade48 (Jan 4, 2008)

Bubbles of gas (regardless of whether they are (pure) oxygen, air, or CO2) will dissolve to some degree as they make their way up to the surface of the water. The dissolution of the gas is mainly dependent on surface area. 

If you are using an air pump and air stone, there will be some air/oxygen that dissolves into the water as the bubble makes it way up to the surface. However, it will be minuscule compared to the increase in diffusion of oxygen at the water/air interface due to the increase in surface area (i.e. the bubbles popping at the surface).


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## WaterLife (Jul 1, 2015)

Darkblade48 said:


> Bubbles of gas (regardless of whether they are (pure) oxygen, air, or CO2) will dissolve to some degree as they make their way up to the surface of the water. The dissolution of the gas is mainly dependent on surface area.
> 
> If you are using an air pump and air stone, there will be some air/oxygen that dissolves into the water as the bubble makes it way up to the surface. However, it will be minuscule compared to the increase in diffusion of oxygen at the water/air interface due to the increase in surface area (i.e. the bubbles popping at the surface).


Right, that is kind of what I was expecting. Pretty much air bubbles would dissolve oxygen a bit as they rise or are in the water column, but not nearly as effective as the dissolved oxygen surface agitation itself creates.

I know people turn on air stones when the lights are off/co2 isn't being injected or needed, but was seeing if there was a alternative way to oxygenate the water enough all day (leaving this means of oxygenation on 24/7) without creating too much surface agitation (so you don't off-gas too much co2) as well as not having to worry about a air pump coming on (I know you can use a automatic-timer) when the lights are off to give your fish enough oxygen (plenty of oxygen when the plants are photosynthesizing with the lights on).

But I guess this thought of air bubbles isn't efficient enough and so it is best to either find the right amount of surface agitation from your filter output or powerhead all day (with it being enough for your agitation to provide enough o2 for your fish at night, while not so much agitation that you lose too much co2), or dose co2 with minimal surface agitation (plants providing o2 from photosynthesis) and turning on a air pump or powerhead for more surface agitation during non lighting/not dosing co2 hours.
Those are pretty much the only efficient ways to go about heavily planted co2 tanks right? Besides colder water (can hold more o2)



Darkblade, you seem knowledgeable on chemistry. While thinking of these air bubbles, I thought of the nitrogen contained in the air, and as we know that plants utilize certain forms of nitrogen.
So I did a little research on air and how plants use it, but this info was only on land based plants and not aquatic/submersed aquarium plants.
The article was saying most plants can't directly intake the Nitrogen gas (N2?), but certain bacteria on the plants can break them down the Nitrogen gas which in turn converts it to a form the plants can intake. Do these or similar bacteria exist in the aquarium? I know of the basic of how the nitrogen cycle works within aquariums (beneficial bacteria and plants), but I am asking if aquarium bacteria can utilize the nitrogen in the air to break that down into food for the plants?
There was some mentioning on the nitrogen atoms bonds being broken and it can then turn into a few different forms (including Ammonia NH3 and Ammonuim NH4+which I know are able to be readily used by plants), but it wasn't too clear on how the bonds were broken.

If the nitrogen in the air can be converted into food for the plants by aquarium bacteria or plants themselves, is there a way to introduce more of the air nitrogen? 
I am thinking it is the same as mentioned about with oxygen dissolving into the water, and so air bubbles are of some effect, surface agitation is much more effective (but then again air is largely nitrogen). 
I assume this is probably inefficient sources of plant "food" and would not rely on this source, but I am just curious about the science of things.


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## MJB13 (Jun 30, 2015)

Nitrogen is (I think) about 350 PPM of "air". The only practical way to get atmospheric nitrogen would be to pump the 999,650 other bits in with it, and let the plant roots sort it out. That would probably make a BIG mess!
The most cost efficient way is to separate/generate the CO2, store it in a cylinder and pump from a in through a diffuser.
It might be possible to build a machine to separate the atmospheric CO2, but the cost would be extremely prohibitive.


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## Raymond S. (Dec 29, 2012)

A factor which I never hear mentioned in these discusions...and thank you darkblade
for stating that some oxygen does desolve from the bubbles...more often than not on
questions on this subject someone always says no/not, they do not so I don't want a conflict and I just let it pass. But I also surely believe that some does. Just a question of how much. Little I suspect...but...in trying to learn how to be honest/w myself it has
come to my attention that I need to re-phrase the questions to allow myself to answer it honestly. So... Does the water in this tank contain more oxygen if I use an air stone and pump in there as opposed to before I put that in there ?
Obviously the answer is yes, when I give myself a chance to answer it honestly.
But that factor which I never see asked/added...I also think it heavily depends on
the level of Oxygen already in the water. If it is at or near a saturation level it likely
won't desolve much if any from the bubbles. I think you understand what I'm talking about here.
True pearling should be near if not pure Oxygen. A tank heavily planted/w fast growing plants will already be near saturation level after the plants have been pearling for a while. Or at least much closer that a tank with few plants in it. And I guess I should add...IMO...


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## chinaboy1021 (May 30, 2003)

The details of the responses here mostly blew past me....that said, to answer your question, yes air (78% nitrogen, 21% oxygen, 1% other gases) from air pump will dissolve into the aquarium, in a similar manner of co2. 

I've been injecting air via air pump into my co2 reactor for 3 minutes at night. It dissolves by the morning. 

I posted a similar thread on your same topic, maybe check it out. I mostly disregarded the responses pertaining to usefulness of actually injecting air into a planted aquarium.
http://www.plantedtank.net/forums/showthread.php?t=898593


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## roadmaster (Nov 5, 2009)

Was discussion /testing performed on ancient website"The Krib" regarding the topic.
O2 meter was used to measure O2 with powerhead's,sponge filter's,airstones, etc and without.
The powerhead's I believe produced more O2 when placed in such a way as to create surface rippling but all method's produced more O2 than without.
I was researching this topic when deciding to raise young Discus and only filtration I provided was from two Hydro V sponge filter's powered by Luft air pump in 55 gal tank.


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## mattinmd (Aug 16, 2014)

WaterLife said:


> Darkblade, you seem knowledgeable on chemistry. While thinking of these air bubbles, I thought of the nitrogen contained in the air, and as we know that plants utilize certain forms of nitrogen.
> So I did a little research on air and how plants use it, but this info was only on land based plants and not aquatic/submersed aquarium plants.
> The article was saying most plants can't directly intake the Nitrogen gas (N2?), but certain bacteria on the plants can break them down the Nitrogen gas which in turn converts it to a form the plants can intake. Do these or similar bacteria exist in the aquarium? I know of the basic of how the nitrogen cycle works within aquariums (beneficial bacteria and plants), but I am asking if aquarium bacteria can utilize the nitrogen in the air to break that down into food for the plants?


There might be some nitrogen fixing bacteria in aquariums, but I don't think this affect is going to be significant. I've certainly never heard of anyone considering using it as a source for plant growth. Even in terrestrial planting, there's only a *very* limited number of plants that can harbor nitrogen fixers to any useful effect.. legumes (beans/peas) and clover come to mind right away as plants that can do this, but the plants that can are very few and far between. (Side note: this is also why clover tends to take over lawns with insufficient nitrogen.) Even in terrestrial gardening, atmospheric nitrogen is generally "irrelevant" when it comes to plant needs.. Fertilizers, composts or other organic matter are pretty much always your nitrogen source. Yes, there is some more nitrogen fixing going on in the soil, but nitrogen being recycled back-and-forth between growing plants and natural composting of dead plants/animal waste is a larger factor. 


On the other hand, back in aquariums, it is well documented that there are denitrifying bacteria that convert nitrate into nitrogen gas which do well in aquariu... which is the *opposite* of what you're looking to do. Most aquarg.iums have very little denitrifying going on unless you're doing a reactor designed for that purpose, but they almost certainly have more of that action than nitrogen fixing.

If your plants need nitrogen, fertilizers like fish waste or KNO3 are by far a better solution.


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## Oso Polar (Apr 22, 2015)

mattinmd said:


> There might be some nitrogen fixing bacteria in aquariums


Oh, definitely! For example, BGA: https://en.wikipedia.org/wiki/Cyanobacteria#Nitrogen_fixation :wink::hihi::hihi:


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## Zapins (Jan 7, 2006)

I feel it is important to take a step back and look at the big picture for a minute when talking about adding oxygen to our tanks. People are often concerned about oxygen in their water and usually do not need to be.










Oxygen does not dissolve in water very well. At aquarium temperatures, 77 F (or 25 C in the chart below), a maximum of 8.6 ppm (same as mL/L) will dissolve into the water. This means that no matter how many bubblers, what size the bubbles are you will never get more than 8.6 ppm oxygen in the water. The only way to have more than 8.6 ppm oxygen in 77F water is to super saturate it using a higher concentration of oxygen than normal air has or increase the pressure on the water above normal room pressure. This is why you often see bubbles after a water change. The water was under more pressure in the water system than it is in your tank, so the excess gas comes out of solution and causes bubbles.

Each species of fish has a slightly different optimal amount of oxygen that should be in the water. Most of the species we keep are in optimal conditions around 5-6 ppm O2. They will not be stressed below about 3 ppm, and will not die until oxygen is between 1-2 ppm. Catfish are much more tolerant of low oxygen conditions and can easily tolerate below 2 ppm without harm. These are day time values when the fish is actively moving around and needs more oxygen. At night time when the fish are asleep and not moving, they need far less oxygen before they are harmed. (numbers quoted from http://www.fondriest.com/environmental-measurements/parameters/water-quality/dissolved-oxygen/#12).

Considering these numbers, it is hard to see the benefit of adding oxygen to the water via bubblers. Our tanks rarely if ever have poor enough circulation to become oxygen deficient under normal conditions. The surface area to volume ratio is huge compared with the surface area to volume ratio of a lake or very large body of water, this fact alone practically ensures you will never have a lack of oxygen. The only time to be concerned about a lack of oxygen is when the temperature rises too high (90-100 F), you have way too many fish in the tank (like the feeder fish tank at the local fish shop) or if there is too much decaying material in the tank (bacteria grow quickly and use up all the oxygen in the water before it can be replaced by the surface). Outside of these conditions adding oxygen is not necessary and may actually disturb fish and deprive plants of CO2 that is jostled out of the water.

On the flip side of this issue is that too much oxygen in the water for a long period of time (super saturated water) can cause fish disease. This is not a common problem, but can happen if you have a constant water change system that is always adding fresh water to the tank and draining old water. I had this issue with my system before tweaking it many years ago. The gas bubbles come out of solution in the tank like normal, but they also come out of solution inside the fish's body and can build up in the blood stream and between their eyes, causing some nasty and potentially fatal conditions. The issue is similar to divers returning too quickly from a deep dive - "the bends."

So, while being concerned about oxygen is commendable it really is not something you need to be concerned with under normal tank conditions. If your fish aren't breathing quickly or gasping then oxygen definitely isn't limited. Even if they are gasping it doesn't always mean low water oxygen. Gasping can also be a sign of other problems.

As for nitrogen fixers in the aquarium, they aren't common and atmospheric nitrogen cannot be used by most plants. In other words, if you do not dose nitrogen in a usable form (fertilizers, soil, fish food/poop) plants will develop nitrogen deficiency fairly quickly. Though for argument sake there is always an exception: I believe aquatic marselia species can nitrogen fix.


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## Hoppy (Dec 24, 2005)

MJB13 said:


> Nitrogen is (I think) about 350 PPM of "air". The only practical way to get atmospheric nitrogen would be to pump the 999,650 other bits in with it, and let the plant roots sort it out. That would probably make a BIG mess!
> The most cost efficient way is to separate/generate the CO2, store it in a cylinder and pump from a in through a diffuser.
> It might be possible to build a machine to separate the atmospheric CO2, but the cost would be extremely prohibitive.


Air is about 80% nitrogen, so air contains about 800,000 ppm nitrogen. Aquatic plants, as well as terrestrial plants can't use N2 as a nutrient. The N2 has to be converted to a plant available form of nitrogen before plants can use it. That can be certain oxides of nitrogen, ammonia, or other more complex compounds.

"Air" doesn't dissolve into water, the various molecules that air is made up of do dissolve, but at different rates. O2 does not dissolve rapidly in water like CO2 does. I'm not sure, but I don't think N2 dissolves at all in water.

Plants take up nutrients as ions, so the plant available forms of nutrients are all either cations or anions, not molecules.


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## mattinmd (Aug 16, 2014)

Hoppy said:


> I'm not sure, but I don't think N2 dissolves at all in water.


It does.. nitrogen gas bubbles coming out of solution in your bloodstream is what causes the bends in scuba divers..

Now that said, it is roughly half as soluble as oxygen.

http://www.engineeringtoolbox.com/gases-solubility-water-d_1148.html


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## roadmaster (Nov 5, 2009)

Zapins said:


> I feel it is important to take a step back and look at the big picture for a minute when talking about adding oxygen to our tanks. People are often concerned about oxygen in their water and usually do not need to be.
> 
> 
> 
> ...


 
Cannot disagree more with most of your theory.
Plant's,bacteria,fishes,all use( lot's of oxygen) to function and good surface ripple/O2 exchange in fish only tank's, or planted tanks,provides benefit's for all life therein . 
Many species of catfish,pleco's,loaches, other riverine fishes as well as other tropical's, appreciate/thrive, in cool water's with High O2 level's.
Will agree that with proper maint of glass box of water where there are no tides,current's,rain, to carry away dissolved solid's,organic waste, that most do not need to worry bout low O2 level's, but taking measures to induce/create a little more O2 does not hurt.
Would rather do this, than expieriment/learn at what point low O2 becomes issue for plant's,bacteria,fishes I keep.
Few tanks,fishes I suspect, function well for long with O2 level's below 3ppm and perhaps even fewer know what level's of O2 are present at any given time in their tank's.
Read a very good article bout biological oxygen demand in the aquarium a few year's ago that was written by a member at UKAPS.org for I believe www.planetcatfish.com.
Not smart enough to provide a link, but some searching might produce some interesting reading?


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## burr740 (Feb 19, 2014)

To the original question, an air stone provides oxygenation in two different ways. One is increased gaseous exchange at the surface (as already mentioned). The other is from the additional circulation created by the stream of bubbles rising up. The bubble stream itself pulls and moves water. Same type of pull that powers a sponge filter. 

So you have water from the lower levels of the tank being moved to the surface, agitated and exposed to the atmosphere, then sent on it's way throughout the rest of the tank, with a now higher oxygen level. As more and more water is "processed" this way, the more oxygen the entire tank gets....up to the point of full saturation of course. That is how an air stone works to oxygenate an aquarium.

As to the benefits, Ive seen enough instances where a whole tank immediately perks up from additional oxygenation - the fish, the plants, everything - that I know beyond a doubt it is beneficial.


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