Previous Discussions On Oxygen Transfer From Air Stone Bubbles

[eaglesaquarium]

The laws of physics don't change but our understanding of them improves over time. If they were only testing a simple process, fine, but anything in-depth and a more recent study would be more relevant

You guys are really going to have to explain to me why more recent means more relevant? How is the topic of the study in question not relevant?!? It studied the amount of gas that diffused out of bubbles in water! That is exactly what is being discussed!

Special relativity was first formulated in 1916 -- yet is still just a relevant as ever. Have you ever used a GPS? If so, you've seen general relativity in action.

Shoot, let's go back even farther. Newton first published Principia Mathematica in 1687, outlining his three laws of motion. Those laws of motion are still just a relevant today, and Newtonian mechanics are used in calculation of every bridge, building, rocket going in space, car, weather prediction, etc. etc. etc. Newtonian mechanics are just as relevant as ever.

Sure, the exact details of gas diffusion into liquid may be known better, but the 1954 paper I cited is not completely overthrown. A newer estimate may be a little more accurate, but that older estimate is no worse than +-5%. There are many processes in production in the chemical industry today based on the estimates in that paper. Virtually any distillation tower with bubble or cap trays uses the estimate from that paper. Virtually any liquid phase reactor uses estimates from that paper. The estimate in that paper has been confirmed as pretty darn good time and time and time again, like general relativity and Newtonian mechanics.

Not to stick my nose into a hornet's nest, but this discussion has finally worked its way into my area of expertise.


To question the validity of an article purely on its date of publication is beyond ridiculous. As Bignose has stated, Newton published his Principia Mathematica in 1687. In 1905, special relativity was published, and then in 1916 general relativity was published. These later writings tweaked what we understood as mechanics, and a new branch of science called relativistic mechanics was born. The work from Newton has actually been superseded by the work of Einstein. And yet when the Apollo missions were being calculated, the NASA scientists used Newton's work, not Einstein's because A) it was simpler, and B) the difference was so minute that it wasn't worth discussing.

In other words, Newton's work back in 1687 was (and still is) just as relevant, even though Einstein's work has changed our understanding of it. The truth is that for macroscopic situations at low speed, Newton's "laws" are still as valuable as ever.


In this argument, unless there has been a giant breakthrough that has completely refuted the previous research (as happened as the model of the atom was being constructed during the late 1800's through the early 1900's) the approximation that was put forth in 1954 is still relevant today. And the order of magnitudes of difference in the oxygen transfer for the surface as compared to air bubbles provided by an air pump is so large that the argument that the contribution by the air stone is anything more than trivial is just denying the science (regardless of what year it was developed).



Now getting back on topic... How do you define a "mature tank"? Is it defined by the maturation of the filter, or is it about all the other ancillary elements working together in harmony? (i.e. could taking a mature filter and placing it into a brand new tank instantly produce a "mature tank" or would it need to run for about 6 months before the tank itself would be considered "mature"?)

 

[Geoff-]

only the top inch of water is oxygenated

I think that this misconception stems from the above one. Since as SbS notes, diffusion will spread oxygen throughout the water. Even it is perfectly stagnant, in about 24 hours even water completely devoid of oxygen will be pretty darn close to equilibrium. There is no reason the oxygen would diffuse in 1 inch and then stop, especially when these is a virtually limitless source in the atmosphere.

I don't pretend to be an expert on this, but "virtually limitless source in the atmosphere" got a chuckle out of me. I guess 21% oxygen will forcefully diffuse itself right through a body of water?

Some quick googling found me a report on mine tailings: click me. Slide 6 shows a graph of oxygen concentration vs depth for stagnant water - which is what we're talking about if you rely on diffusion only. At 1 metre depth you are talking about 2g/m^3 of oxygen and at the surface it is 8g/m^3. That is a significant difference in only 1 metre of water, and a LONG way from the "oxygen diffuses instantly" argument that is being put forward here. Even half a metre down, the oxygenation level has dropped by 40%. Which brings me back to the point that an air stone will lift this water up to the surface where it can be more efficiently oxygenated. Diffusion alone isn't sufficient to guarantee a completely oxygenated aquarium even at a depth of only 0.5 metres.

I think the whole issue of diffusion is largely irrelevant given we want our filters/airstones to actually stir the water.. but while we're debating each point we might as well address this one.

The laws of physics don't change but our understanding of them improves over time. If they were only testing a simple process, fine, but anything in-depth and a more recent study would be more relevant

You guys are really going to have to explain to me why more recent means more relevant? How is the topic of the study in question not relevant?!? It studied the amount of gas that diffused out of bubbles in water! That is exactly what is being discussed!

Special relativity was first formulated in 1916 -- yet is still just a relevant as ever. Have you ever used a GPS? If so, you've seen general relativity in action.

Shoot, let's go back even farther. Newton first published Principia Mathematica in 1687, outlining his three laws of motion. Those laws of motion are still just a relevant today, and Newtonian mechanics are used in calculation of every bridge, building, rocket going in space, car, weather prediction, etc. etc. etc. Newtonian mechanics are just as relevant as ever.

Sure but let's go back even further. We used to think the world was flat and the earth was the centre of the universe. We are *always* improving our understanding. Some aspects (Einstein, Newton) hit the nail on the head and have not been challenged but other observations have been incorrect. Likewise, theories about the nitrogen cycle in aquariums are always being changed as we learn more. We always used to think Nitrobacter was what dominated aquariums but recently Nitrospira was shown to be the strain to have. There is still literature floating around saying Nitrobacter is important but believing it because you see one report is foolish. All we are arguing here is that you really can't tell the authenticity (good or bad) of an article by its age

Apologies if I come across as cynical, I haven't read enough of your posts to consider you a trustworthy source. You've since said that the 1954 report is used industry-wide, which makes it a whole lot more noteworthy than 1 person on the internet saying "this report from 1954 says....." (no offence).

it isn't a question of 'win', it is a question of describing the situation accurately, and representing the physical processes that are occurring. It is not a question of 'win', it is a question of expanding knowledge. I fully concede I could be way wrong on this, but the resources I have access to and knowledge of show that predicted amount of gas exchange from even hundreds of bubbles is very tiny compared to the exchange at the tank top surface. All I can go by are the resources I have, and my experience with how well the predictions based on these resources have worked in the past. If someone has other resources to show me, I am always eager to expand my knowledge. But at this time, I am going to stick with what I know.

Fair comment, and I think your original point about the bubble surface area not contributing much to overall oxygenation is also logical. However, the overall effect of a bubble curtain is that it:
1) oxygenates the water directly by increasing the surface area (small effect)
2) agitates the surface of the water as bubbles burst, increasing the exposure of the water to the air (possibly large effect)
3) draws deoxygenated water from the base of the tank up to the surface so that the oxygen can be replenished at the water surface (large effect).

So saying that air stones don't work because the surface area created is ignoring most of what's going on. Sure, the surface area of the bubbles is small but it's a bit secondary to everything else that's going on. If your filter already stirs the tank water properly then an air curtain won't achieve a thing besides looking pretty. That, I think we can all agree on!!

Not to stick my nose into a hornet's nest, but this discussion has finally worked its way into my area of expertise.


To question the validity of an article purely on its date of publication is beyond ridiculous.

Careful now - I didn't say it was meaningless because it was old just that a newer study may be more relevant. That was without knowing the contents of the report and how widely it was referred to in industry, something Bignose has now said. Sure, if it is an industry-wide acccepted situation and is on par with Newtonian physics and Einstein's relativity then it's pretty well irrefutable. 1 person on an internet forum saying that a report in 1954 said XYZ really doesn't carry any weight with me, as a standalone statement.

One must be careful when making general statement's for there are many variables to consider in my humble opinion.

Agree 100%. There is a lot going on in a tank and we must be careful we're not ignoring other processes.

 

[Bignose]

I don't pretend to be an expert on this, but "virtually limitless source in the atmosphere" got a chuckle out of me. I guess 21% oxygen will forcefully diffuse itself right through a body of water?

Some quick googling found me a report on mine tailings: click me. Slide 6 shows a graph of oxygen concentration vs depth for stagnant water - which is what we're talking about if you rely on diffusion only. At 1 metre depth you are talking about 2g/m^3 of oxygen and at the surface it is 8g/m^3. That is a significant difference in only 1 metre of water, and a LONG way from the "oxygen diffuses instantly" argument that is being put forward here. Even half a metre down, the oxygenation level has dropped by 40%. Which brings me back to the point that an air stone will lift this water up to the surface where it can be more efficiently oxygenated. Diffusion alone isn't sufficient to guarantee a completely oxygenated aquarium even at a depth of only 0.5 metres.

Geoff, your link there is irrelevant, because it is not the same situation. There is a huge sink of oxygen in those tailing pools where the waste at the bottom is consuming oxygen. The diffusions through the water is due to there being a huge source at the atmosphere and a huge sink due to the mining waste consuming it.

And, yes, the atmosphere is a huge source. Even though oxygen is only 21% of the air, think of just how much atmosphere there really is. Basically, there is a virtually limitless source of argon, even though it is only 0.93% of the composition of air, because there is such a large amount of air. It isn't that it is 21% or 0.93%, it is that there is so much.

So, comparing the waste diffusion slides with a fish tank are way wrong. Fish tanks don't have anywhere near the sink of oxygen that that mine waste does. Fish are about the only sinks, and they aren't a very huge sink unless in extra ordinary circumstances. Fish can survive in tanks because the surface gives so much oxygen to the tank.

Furthermore, the slides from the mine waste aren't comparable, because we know fish live in water, even stagnant water, more than 1 m down. If there was really only 60% of the oxygen available, no fish would be able to live in it. That is not enough oxygen to support fish life.

In a body of water without huge consumers of oxygen, the diffusion rate is such that the water will be at equilibrium -- fully saturated with oxygen -- in a matter of hours.

Apologies if I come across as cynical, I haven't read enough of your posts to consider you a trustworthy source.

This is fine. I will always defend a skeptic, and I will always provide my sources when I can. I do have quite a lot of posts on this forum you can read if you want to see my body of work. I think I've posted pretty much the same way since day one, and it is part of the reason I am the appointed head of the Scientific Section sub forum. But, I wouldn't be a good scientist if I just told you to take my word for it -- so feel free to ask me to back up any statement I make, and I'll do my best to do so. I may not always be able to back it up immediately because it may take me time to look up the sources I've used before, but I'll get to it in the end.

We are *always* improving our understanding.

Sure, but unless there is a huge reason to think the original experiment was done wrong, I still don't get the reluctance to accept its results simply because of its publication date. I mean, again, it was a study on measuring the amount of gas diffusing out of bubbles! That is exactly what we're talking about. Unless there is a major reason to think it was wrong, it doesn't matter what year the results are from.

This is a topic that really gets to me because in today's Internet society, people really have a bias -- whether acknowledged and conscious or not -- that the only information that is any good is recent. And anything old doesn't have meaning. This isn't just younger students, either, but advanced college and graduate students that should know better who show reluctance to go to the library and photocopy an older article when it isn't available to download off the Internet. Missing out or rejecting a huge body of work is just foolish. Today's science is literally standing on the shoulders of the giants before us, and being unfamiliar with the previous work -- especially those doing it deliberately -- are just shooting themselves in the foot. But, I digress.

 

[eaglesaquarium]

Today's science is literally standing on the shoulders of the giants before us,

Does anyone know the original person to utter these words?

Isaac Newton famously remarked in a letter to his rival Robert Hooke dated February 5, 1676 that:
"What Descartes did was a good step. You have added much several ways, and especially in taking the colours of thin plates into philosophical consideration. If I have seen a little further it is by standing on the shoulders of Giants."

But, that was not the first recorded statement. The first is considered to be: Bernard of Chartres in the mid-1100s.

The attribution to Bernard is due to John of Salisbury. In 1159, John wrote in his Metalogicon:[2]
"Bernard of Chartres used to say that we are like dwarfs on the shoulders of giants, so that we can see more than they, and things at a greater distance, not by virtue of any sharpness of sight on our part, or any physical distinction, but because we are carried high and raised up by their giant size."

Not to drive the topic further off course, but you are dead on accurate. Today's young people have a definite lack of appreciation for the things that came before them. Other work from that same era has laid the groundwork for much of the technology that we now enjoy on a daily basis.

 

[Geoff-]

Geoff, your link there is irrelevant, because it is not the same situation. There is a huge sink of oxygen in those tailing pools where the waste at the bottom is consuming oxygen. The diffusions through the water is due to there being a huge source at the atmosphere and a huge sink due to the mining waste consuming it.

Fair call, I didn't consider chemical processes in the substrate.

We are *always* improving our understanding.

Sure, but unless there is a huge reason to think the original experiment was done wrong, I still don't get the reluctance to accept its results simply because of its publication date. I mean, again, it was a study on measuring the amount of gas diffusing out of bubbles! That is exactly what we're talking about. Unless there is a major reason to think it was wrong, it doesn't matter what year the results are from.

I accept that diffusion out of a gas bubble is going to be a very small influence. In the context of this thread, yep, the bubbles do nothing. But in an actual tank the stirring caused by an upwell of bubbles will help oxygenation in a borderline case. I don't run an air stone in my tank, there is no need. But if I had a failed filter then I'm sure an air stone would be very helpful.


I found one of your other comments earlier in the thread interesting:

In order to encourage biodiversity, I actually change the heater settings on my tanks every 6 months or so, just so that no one group becomes too dominant.

This either makes your tank more hardy because of increased biodiversity, OR it makes it more hardy because it exposes the fish to a natural variation in temperature (which will happen seasonally in the wild, if not daily). If you were kept in a chamber at 24C for a year and suddenly exposed to 18C it would probably come across as a bit of a shock. But if you regularly cope with temperature swings (and those swings aren't wild enough to cause undue stress) then a single cooling event is less likely to affect you because your tolerance is good. I'm sure the same thing happens with fish, as long as you don't go outside their recommended temperature range.

 

[fishguy2727]

Nature may not have changed since 1954, but our research methods, technology, etc. sure have. I have read through enough scientific articles to know that even scientists can be less than 100% accurate in their methods, reasoning, etc. Something from 1954 could be errored. I don't know but I am guessing a more recent and possibly much more accurate study has been carried out. To rely on studies from the 50s as the only information considered is not the best idea IMO.

With all this theoretical back and forth or not, I have seen the difference even a single air stone can make I believe the results are from more than the increased flow. The diffusion happens almost instantly, otherwise we could have too much flow at the surface and oxygen wouldn't have enough time to cross at the tank's surface either. You don't have to believe me, obviously some people won't. But IME the aeration and gas exchaneg provided by an air stone are more signficant than water flow.

 

[Bignose]

Something from 1954 could be errored.

Sure, it COULD. Heck, anything COULD be errored. That doesn't really say much. Is there any actual reason to believe it is errored other than "it could be errored"?

For that matter, you might at well stop reading any scientific paper, because they all COULD be errored. In fact, a great majority of them well be errored, as we learn greater and greater things as time goes on. You probably will want to wait until all science is done and every single experiment has been done and every single question as been answered -- it is the only way to be sure that the results COULDN'T be errored.

Sheesh.

Ok, I guess I give up. Nothing is going to convince you otherwise anyways, even though I've presented a wealth of evidence on my side and I see no evidence presented for your side. Rationality doesn't win in favor of a paper that COULD be wrong because it is old. I am still open to changing my mind if evidence can be presented, but I am not just giving up on known good research just because it COULD be errored.

 

[fishguy2727]

I got an excerpt of the paper. I didn't see methods, data, etc.

It is not just could, it probably has been done more thoroughly and with more advanced equipment and techniques than 1954. All I am saying is that there is more information available than one study from 1954 so that one study along cannot disprove anything.

As stated, my own experience tells me that the bubbles themselves do provide a lot of aeration. Common sense says that if there is a minimum contact time required for oxygen to diffuse across the air-water surface than it is possible to have too much flow at an aquarium's surface, which is obviously not true. Air and water moving past eachother creates aeration, regardless of which one is moving or moving faster. If you don't believe it you don't have to, but I am not going to go against what I have seen because of one paper from 1954.

 

[StandbySetting]

From experience? Do you have viable methods of measuring the concentration of Oxygen within the water column?

http/www.smbc-comi...s&id=2159#comic
courtesy of Bignose

 

[eaglesaquarium]

As a science teacher, this type of response would get an F on a science paper. To posit that a study should be discounted on the grounds of when it occurred is just ludicrous. If you want to question their methods, do it, but use specifics. If you want to put forth a competing research study, then do it. But, to merely dismiss it out of hand because "methods, technology, etc. have changed"? You are in no way addressing this from any type of standpoint that could even be remotely called "scientific". You are merely covering your ears and saying "La la la, I can't hear you", because you disagree with the findings. To disagree is fine, but you have nothing to support your position. You mention your experience, but have nothing concrete in a quantifiable regard to offer as objective proof beyond your "word" that it is true.

This exchange regarding the validity of a scientific study centering on the date of the study is a sad commentary on the understanding of science. Not to mention the fact that the technology of that era (ok, about 15 years later) was sophisticated enough to get man to the moon. Going back further, the technology used by astronomers of the 1600's used VERY rudimentary equipment by today's standard, but that equipment was sufficient to get to the proper heart of the matter - planets orbit the sun in ellipses (close to circles). The truth is that while the scale may vary the general finding is (probably) valid. If you want to find a newer study that offers evidence that supports your position, that's fine. But, if not, stop questioning this study based solely on the date of publication. The date that a study was done is not a reason to question something. And to throw generic barbs out there, that the experimenters "may" have made errors is akin to my students using the standard "human error" excuse for why their results are not more in line with accepted findings. Acceptable errors (which are not mistakes according to the usage by a scientist) would be either procedural or equipment limitations in taking measurements. For example, when timing someone running a 100 meter dash, an acceptable error would be the reaction time of the person operating the stopwatch (roughly 1/7th of a second), whereas the student claiming that they may not have clicked the button at the wrong time would be unacceptable. Please offer a similarly credible study to support your position.


********

Getting back on target with the nature of this thread... Is the "mature" nature of the tank related to the filter or is it related to ALL the parts? I asked this a while ago, but would moving a filter from a "mature" tank to a brand new tank mean that the new tank is now "mature as well, or will it take more time than that to get "mature"?

 

[fishguy2727]

A quick google search produces multiple sources citing how the bubbles themselves increase aeration and oxygen exchange. I know wikipedia should not be considered over scientific articles, but the page on water aeration has multiple mentionings of oxygen exchange in bubbles, how smaller bubbles increase aeration, etc. I can't get to any of the resources to find a more reliable source, but the cited information (not made up, but actually came from somewhere besides wiki) includes:
"The EPA defines a fine bubble as anything smaller than 2mm in diameter.[5] This type of aeration has a very high oxygen transfer efficiency (OTE), sometimes as high as 15 pounds of oxygen / (horsepower)hour"

"By releasing millions of fine bubbles instead of fewer coarse bubbles, fine bubble diffused aeration is able to maximize the surface area of the bubbles and thus transfer more oxygen to the pond per bubble. Additionally, smaller bubbles take more time to reach the surface so not only is the surface area maximized but so are the number of seconds each bubble spends in the water, allowing it more time to transfer oxygen to the water. As a general rule, smaller bubbles and a deeper release point will generate a greater oxygen transfer rate."

I know this is wiki, and you will probably take that as more than enough to disregard it, but obviously somewhere along the way people figured out that bubbles themselves provide aeration, regardless of what a 1954 study claims.

 

[Bignose]

Common sense says that if there is a minimum contact time required for oxygen to diffuse across the air-water surface than it is possible to have too much flow at an aquarium's surface, which is obviously not true.

Right, it isn't true because equilibrium is reached. Oxygen doesn't just continue to pour into the surface because there is surface there. What does happen is oxygen very quickly reaches the equilibrium point between the amount dissolved in the water and the amount in the atmosphere. The exact value is determined by atmospheric pressure, and the water temperature and salinity. But, the reason equilibrium is achieved rapidly is because of the large amount of surface area at the top of the tank, not because of the bubbles.

You cannot argue that because an equilibrium is reached, that the bubbles much therefore be significant. By my estimates, the bubbles do almost nothing for moving toward equilibrium.

Your "common sense" forgot about equilibrium, which is why common sense cannot be trusted when doing science. Common sense isn't always right, and sometimes is flat out wrong. The only thing science is based on is the evidence, like say that published in papers, even if they are 60 years old and not believed simply because they are old by people on the internet.

(Would it help if I showed you the derivation of their equations from first principles? Because I can. The experiment they did was just to show that their derivation from first principles is actually pretty darn good when compared to experiments. The first principles that went into the equations haven't changed. They are the Navier-Stokes equations of fluid mechanics and Fick's law of diffusion. But those were probably derived too old for you to believe in them, too, right, seeing as they are over 100 years old each.)

Regarding "By releasing millions of fine bubbles..." you do realize that there is a difference between millions of bubbles and the hundred or so a typical aquarium air stone puts out, don't you? You get an airstone with millions of bubbles, then we can talk. But, I've never seen one in an aquarium. My conclusions above are based on there being at most thousands of bubbles in the water, which is still 4 orders of magnitude of surface area less than a small tank top surface area.

 

[fishguy2727]

Millions of bubbles are needed for a pond, not an aquarium.

Anyways, obviously no talking to you. You can stick with one paper from 1956, I will be fishkeeping in 2011.

 

[Bignose]

Millions of bubbles are needed for a pond, not an aquarium.

When was a pond ever mentioned? Everywhere, my estimates were for a typical aquarium. If indeed it is in a pond, then millions may not be enough again because the surface area of a pond is quite a lot larger than the surface area of a 10 gallon tank, and I suspect that top surface area will be orders of magnitude larger than even millions of bubbles

You can stick with one paper from 1956, I will be fishkeeping in 2011.

Keep fish however you want, you sure aren't doing science in 2011, or at least critiquing sources. People make mistakes, and think that bubbles lead to large amount of gas transfer. It's okay to make mistakes, we all do it. I fully concede that my own position on this could very easily be in error -- but I want to see a good argument against what is my current position. I don't think that that is too much to ask. Right now I have equations derived from first principles and results from an experiment in agreement with that derivation. It certainly could be wrong. But until there is good reason to think it is wrong, I'm sticking with the known results. Your "common sense" is not enough to over throw results known to be good -- even if old.

Speaking as moderator here, unless you do have some evidence to rebut the evidence I've provided, I think that this thread has just about run its full course. I'm going to leave it open for a short time for other to respond if they want, but otherwise, I think I'm going to close it shortly. I don't see a good reason to leave it open.

 

[Mikaila31]

WOW guys... bubbles are more annoying now then before I read this thread .

Mature tank is personal opinion. I will agree that a 'biofilm' is important, but its importance also varies from tank to tank. If you have a bare bottom tank with minimal decore your pretty low on much stuff going on outside the filter. I've not had a problem setting up tanks and adding a full stock of sensitive fish within hours then cloning the tank. Such a tank is entirely dependent on the filter. I currently run 2 'el natural' tanks that are not filtered. A 15 gallon with about 30 fish and a one gallon with a DP. The latter is entirely stagnant. Both I consider mature tanks because they are stable. Both have been stable since the day they were setup having never registered any ammonia or nitrites. They do not rely on the typical bacteria cycle, there is still a cycle going on but its different. The 15 gallon is at least 6 months old and has yet to have even a minor algae problem.

I just in the end what I consider a mature tank is a balanced STABLE tank. I don't care how its done. I've done it many ways with success in keeping fish. No two tanks are the same. That bare bottom tank NEEDS its filter. Most of my current tanks either don't use a filter or can have their filter turned off for a couple days without a problem.