Importance of aquarium aeration

[jjohnwm]

I was under the impression airstones couldn’t atomize air down to a level of enacting a molecular change in anything. Thought it was for agitation of the water surface……..movement…….and to increase flow throughput/bacteria surface if used in conjunction with a sponge filter or under gravel system.

Well, the most correct definition of "atomize" is to reduce something to its component atoms. That certainly isn't happening due to bubbles in an aquarium, regardless of how small they are. Something is also said to be "atomized" if it is broken down into extremely small particles, and this poorer definition is sort of what is being discussed here.

Smaller bubbles are more efficient than big ones simply because the same volume of air is now exposing much more surface area to the water for gas exchange. Again, no molecular change occurring. Air is simply a mixture of gases...which are present in the mixture as molecules, not individual atoms...and we are trying to facilitate the movement of oxygen molecules (each a pair of oxygen atoms) into a dissolved state in the water and the movement of carbon dioxide molecules (each a single carbon atom and a pair of oxygen atoms) out of the water.

I just don't think that the combined surface area of all those bubbles is that significant compared to the surface area at the top of the tank; maybe I'm completely wrong about this. I am convinced that the major benefit of the bubbles is the circulation of water that they produce, bringing all of the water into eventual contact with the surface; the surface area of the bubbles works just like that surface at the top, but I think it's too small to make much of a difference in and of itself.

Try an experiment. In the past, I have done the hack F fishdance mentioned, i.e. using an inflated air mattress as an emergency air source for a fish tank. It worked fine...although the tanks that didn't have one also were fine. Now, I suspect that the air in that air mattress was largely depleted of oxygen and especially rich in carbon dioxide, based upon the fact that I blew the mattress up by mouth and nearly passed out several times while doing so.

If those bubbles were effecting much of a change due to their own surface area, it would have been likely a negative one (i.e. adding CO2) rather than the positive one I was aiming for. If that did happen, it wasn't enough to bother the fish. But there is no denying that the stream of bubbles did indeed circulate the water, as the temperature remained stable throughout the tank, whereas tanks left completely unaerated quickly stratified with the surface water much warmer than that below. By the same token, my outdoor stock tanks in the summer remain livable for the fish only if I do not aerate them, allowing them to stratify so that the fish can find a comfortable temperature level during hot weather. Drop an airline or sponge filter in, as I did...thinking I was being oh so clever...mixed the water enough that the entire tank became too warm and I nearly lost a number of fish.

All of that combines to convince me that the water motion created by bubbles is far more important than the gas exchange on the surface of the bubbles themselves.

 

[esoxlucius]

I remember a time, a long time ago in my defence, lol, when I thought that oxygen in a fish tank came solely from the bubbles created by those quaint little treasure chest, ship or little diving guy ornaments.

What drove me crazy though was how could those bubbles provide oxygen to the water when no sooner had the bubbles been generated, they'd hit the surface of the tank and gas off!!

In time I learnt that it was nothing to do with the actual bubbles themselves, but the agitation they caused when hitting the surface en masse.

Bubbles are still a common way of generating this surface agitation, thankfully the quaint little ornaments less so, lol.

All my surface agitation is provided by power heads now. The surface is always on the move. And even if I didn't have power heads my water is always rich in oxygen because of my sump which is a crate tier system. Water gushes through there at a rate of knots picking up oxygen on the way.

I'm not really understanding why this thread seems to have taken a complex scientific turn, because in my eyes it's pretty simple stuff really.

 

[Backfromthedead]

I'm simply saying an airstone provides additional surface agitation throughout the water column. I don't know how anyone can argue that. yes it is simple...simple science.

What I'm arguing against are the dim ones who claim the bubbles do nothing at all in exchanging gases. If you're gonna make these claims I'm afraid I do need to see some evidence to back up this simple minded theory.

 

[FJB]

I think something is being underestimated here:
- The main value of aireation via air bubbles is NOT that the bubbles themselves off-gas into the water while they travel up through the water column. In fact, they do very little of that (minimal)
- The main value is also NOT that the bubbles off-gas at the surface (where the higher concentration of O2). In fact, this offgassing at the surface helps the tank water very little),
- Finally, the main value is is NOT the surface agitation produced by the raising column of air bubbles, although the more agirtation the better.

Of the three listed above, the most important is the third. That is, the surface agitation produced by the rising column of air bubbles, which increases gas exchange at the surface.
However, a fourth, and far most important effect is this: A rising column of bubbles creates a circular motion up and down OF WATER (not of air) throughout the water column, such that water from the bottom rises to the surface, exchanges gases there, and sinks back down due to a steady supply of rising bubbles bringing more water from below. This convection current is constant under constant aireation, and is the most important effect of airation in a fish tank "aireated" via air pumps.

In the absence of air pumps, most gas exchange still occurs at the surface, but it is not due to to the convection currents of water produced by aireation. Instead, equivalent (although not always equally convective) currents are being produced by a wavemaker or another type of power filter or otherwise water moving device.

 

[phreeflow]

Don't understand your logic here....the air in bubbles is somehow inferior to the air that agitates the water surface?

Couldn't disagree with you more about the efficiency issue. Airstones themselves create surface agitation and air pumps are much more efficient than power filters or wavemakers in terms of power usage, and are much less prone to spontaneous failure ime, usually weakening gradually instead of seizing up like a pump or wavemaker.

There's also something to be said for the "upwelling" effect an airstone provides, saturating all levels of the tank with aerated water vs concentrating o2 rich water at the top.

No need to get upset…we are not in disagreement. Was simply just stating that most of the gas exchange happens at the surface, not due to contact with the bubbles. Therefore, it’s more efficient regardless of how surface agitation is created.

Never talked about cost of electricity, or discussed which method was best, or compared which types of filters or methods are prone to failure. In fact, I think aerators are great.

Just want to dispel the notion that every tank needs an aerator. Whether a power head, wavemaker, or hob filters…they all do fine agitating they surface for gas exchange.

 

[eon aquatics]

With a decent air pump and airstone, the amount of surface is increased significantly which in turn creates much more area for gas exchange. And when I say surface, I mean both the surface area around the bubbles hitting the surface and the volume of air travelling through the water column along with the original surface area of the tank.
Adding to the area of tank water meeting air will increase gas exchange, whether this is by airstone, wave maker, filter splash return, spray bar, trickle filter, etc. etc. some are more efficient than others (both cost wise and effectiveness) but at the end, the most efficient is the one which provides the largest air to water surface area over time, along with water movement.

As for planted tanks, the concept of co2 feed imo is purely a financial one. Co2 costs money, so making the bubbles the most efficient size relative to the time they spend in the water allows for the maximum exchange of co2 at the minimum cost. If bottles of co2 were free then we could just as easily pump bigger bubbles and more of them the same way we do with airstones and “throw away” semi depleated bubbles to atmosphere, BUT this then is also counter productive as we also increase the surface area and add more oxygen.
Much of the discussion over which is better, needed, best, etc. comes down to the individual, the individual tank, a cost factor, but mainly the stocking level and how much agitation is required.

i agree

 

[Backfromthedead]

I think something is being underestimated here:
- The main value of aireation via air bubbles is NOT that the bubbles themselves off-gas into the water while they travel up through the water column. In fact, they do very little of that (minimal)
- The main value is also NOT that the bubbles off-gas at the surface (where the higher concentration of O2). In fact, this offgassing at the surface helps the tank water very little),
- Finally, the main value is is NOT the surface agitation produced by the raising column of air bubbles, although the more agirtation the better.

Of the three listed above, the most important is the third. That is, the surface agitation produced by the rising column of air bubbles, which increases gas exchange at the surface.
However, a fourth, and far most important effect is this: A rising column of bubbles creates a circular motion up and down OF WATER (not of air) throughout the water column, such that water from the bottom rises to the surface, exchanges gases there, and sinks back down due to a steady supply of rising bubbles bringing more water from below. This convection current is constant under constant aireation, and is the most important effect of airation in a fish tank "aireated" via air pumps.

In the absence of air pumps, most gas exchange still occurs at the surface, but it is not due to to the convection currents of water produced by aireation. Instead, equivalent (although not always equally convective) currents are being produced by a wavemaker or another type of power filter or otherwise water moving device.

Awesome explanation. Thank you sir.

 

[Fishman Dave]

I think something is being underestimated here:
- The main value of aireation via air bubbles is NOT that the bubbles themselves off-gas into the water while they travel up through the water column. In fact, they do very little of that (minimal)
- The main value is also NOT that the bubbles off-gas at the surface (where the higher concentration of O2). In fact, this offgassing at the surface helps the tank water very little),
- Finally, the main value is is NOT the surface agitation produced by the raising column of air bubbles, although the more agirtation the better.

Of the three listed above, the most important is the third. That is, the surface agitation produced by the rising column of air bubbles, which increases gas exchange at the surface.
However, a fourth, and far most important effect is this: A rising column of bubbles creates a circular motion up and down OF WATER (not of air) throughout the water column, such that water from the bottom rises to the surface, exchanges gases there, and sinks back down due to a steady supply of rising bubbles bringing more water from below. This convection current is constant under constant aireation, and is the most important effect of airation in a fish tank "aireated" via air pumps.

In the absence of air pumps, most gas exchange still occurs at the surface, but it is not due to to the convection currents of water produced by aireation. Instead, equivalent (although not always equally convective) currents are being produced by a wavemaker or another type of power filter or otherwise water moving device.

Not sure if I could actually disagree more.

The science behind oxygen transfer and airation using a decent sized air pump contradicts this completely.
Yes it is important that water containing depleated oxygen is in contact with air, and so water from around the tank needs to get to the surface or in contact with air.
In a completely still aquarium the transfer of oxygen is minimal because oxygen struggles to enter the water at the boundary layer between water and air. To aid this process we create turbulence at the surface. The increase in surface area is beneficial but the turbulence much more so.
By adding thousands of small bubbles of air to the water column we are creating that turbulence throughout the water in the tank, same principle and hence the transfer of gases happens around each and every bubble. There are scientific paper written specifically measuring the amounts and efficiency.
Anyone who owns a koi pond with huge turnovers and circulation of water already happening knows the benefits of adding airstones in hot weather and knows its nothing to do with turning the water over. It’s all to do with the added oxygen from the millions of bubbles themselves turbulently travelling through the water column.

Maybe read “Impact of Bubble and Free Surface Oxygen Transfer on Diffused Aeration Systems”, DeMoyera et. al. 2003: or
“Effect of Bubble Size on Aeration Process”. Navisa, 2014, Asian Journal of Scientific Research, 7: 482-487.

now are airstones needed?
In many situations probably not because sufficient transfer is already happening.
However, for oxygen loving fish, overstocked tanks and hot weather, then my answer would be yes.
Can I convince everyone here, no, but I don’t have to, I use them in some situations and can see and firmly believe the benefits they provide, because I can see and understand the science behind them.

just to finish, I don’t mind if folks disagree, it makes me go read up more and either confirm my thinking (like here) or helps me learn differently.

 

[Backfromthedead]

Not sure if I could actually disagree more.

The science behind oxygen transfer and airation using a decent sized air pump contradicts this completely.
Yes it is important that water containing depleated oxygen is in contact with air, and so water from around the tank needs to get to the surface or in contact with air.
In a completely still aquarium the transfer of oxygen is minimal because oxygen struggles to enter the water at the boundary layer between water and air. To aid this process we create turbulence at the surface. The increase in surface area is beneficial but the turbulence much more so.
By adding thousands of small bubbles of air to the water column we are creating that turbulence throughout the water in the tank, same principle and hence the transfer of gases happens around each and every bubble. There are scientific paper written specifically measuring the amounts and efficiency.
Anyone who owns a koi pond with huge turnovers and circulation of water already happening knows the benefits of adding airstones in hot weather and knows its nothing to do with turning the water over. It’s all to do with the added oxygen from the millions of bubbles themselves turbulently travelling through the water column.

Maybe read “Impact of Bubble and Free Surface Oxygen Transfer on Diffused Aeration Systems”, DeMoyera et. al. 2003: or
“Effect of Bubble Size on Aeration Process”. Navisa, 2014, Asian Journal of Scientific Research, 7: 482-487.

now are airstones needed?
In many situations probably not because sufficient transfer is already happening.
However, for oxygen loving fish, overstocked tanks and hot weather, then my answer would be yes.
Can I convince everyone here, no, but I don’t have to, I use them in some situations and can see and firmly believe the benefits they provide, because I can see and understand the science behind them.

just to finish, I don’t mind if folks disagree, it makes me go read up more and either confirm my thinking (like here) or helps me learn differently.

I wouldn't disagree with anything at all, only add that I think F FJB was stressing the importance of the water movement created by an airstone that mixes and saturates the tank with oxygen rich water so effectively. Natural stratification of oxygen in the water column may be minimal in our relatively small tanks, but in the koi pond example you mentioned becomes quite significant imo.

Catastrophic Oxygen Depletion in your Koi pond

Catastrophic Oxygen Depletion in your Koi pond

aquameds.com

 

[duanes]

I have not used aerators (air stones) in 20 years, except for travel, when I'll add a battery operated pump with an air stone to a bucket when collecting, or extended car travel, or.....if a water pump breaks down, or power goes out.

But both serve the same purpose in agitating the air water interface to promote gas exchange.

As with everything else in keeping fish, I believe the choice has more to do with the kind of fish kept, more than anything else.
If placid water fish are kept, air stones are adequate, they draw water up from a localized area near the substrate, without creating too much flow that could push these type fish around, those that have evolved to live in slack, placid water conditions. Examples might be some Anabantoids, cichlids like discus, or angels, some placid water killifish.

Above 2 killifish species I have kept in low flow enirons
Fundulopanchax sjoestedti left, Pachypanchax playfairi right.

On the other hand, if riverine fish are kept, that have evolved to live in moderate to strong laminar flow, moving quickly on one direction across the length of a tank, or those species from riffles and rapids that require much more water movement, and dissolved oxygen, I prefers of a strong water pump.
Flow
examples might be Geophagines, Tomocichla, Chuco, or stream evolved barbs like Denisons, Congo river inhabitants like Tigerfish, or Telegarmma, or surf dwellers like Eretimodus. In many case the body and fin shape suggests water flow preference.

Chuco micropthalmus left, Geophagus altifrons middle, Tomocichla tuba right.
But, both lots of bubbles and flow can be created by using a simple non-moving part venturi injector if both are desired.

Left a venturi attached to the flow direct to tank, right the venturi, attached to a fractionation unit, used to create lots of bubbles in a column to remove DOC