Oxygenation Of Water

[backtotropical]

This came up in another thread recently and a small discussion took place, but i'd like to get to the bottom of it (or at least get lots of opinions).

In short, i think a powerhead is far superior for the purpose as it will disturb a lot more of the surface (all the surface in some cases) and constantly brings lots of fresh water to the top which means all the water in the tank is constantly being turned over and oxygenated, which an airstone can't do nearly so well.

The air bubbles on the surface which an airstone creates do increase surface area, theres no denying that, but more so than a powerhead pounding away at the surface? I don't think so. What do you think?

Please discuss.

 

[Colin_T]

an airstone bubbling away quite strongly works just as well if not better as far as I am concerned. Even air coming straight out of airline makes a difference.
I prefer airbubbles rather than power heads because one big airpump can aerate numerous tanks and is cheaper than buying and running one water pump per tank.

 

[Bignose]

back, I don't think that it truly matters one way or the other, because unless there is some serious oxygen consumption going on in the tank, both will be more than enough to ensure good oxygenation of the water. When there is a below equilibrium amount of oxygen in the water, the air is very quick to give up some oxygen to put it back in to the water. It would have to be a very still tank to get the oxygen level much below 95% saturation, for example. So, while I suspect that you are right that a powerhead disturbs more which leads to better transfer at the top, it actually probably doesn't matter since it is highly unlikely that you need a massive amount of exchange anyway.

 

[CFC]

The thing is what are we comparing here? A powerhead will probably aerate more water faster than a tiny little toy town air pump but if we are comparing flow rates then a decent air pump pumping 45 litres per minute of air through a large airstone will litterally push water out of a 30 inch high tank it produces so much force (i know, i've done it and got wet), the equivilent would be a 2700 litre per hour powerhead. An airstone produces as much if not more lift than a powerhead but what it doesnt have is directionality, the bubbles can only go up. I dont know if there is any way to actually measure which method is expanding the surface area more but my money would be on the air pump.

As it stands i use both methods, my filtration is all air powered and provides aeration while powerheads provide currents in tanks with fish that need it.

 

[purplekaz]

I can't really add to the scientific arguements for either side here, but I did notice my fishless cycle improved when I turned on the bubbles for longer every day. You can actually see the bubbles bursting at the surface and pushing air down into the water as they pop.
Looking closely at the water in the tank, I can see teeny weeny little bubbles of air just below the surface, much like what you see straight after a water change (well I do anyway, water from my cold tap is so full of tiny bubbles it's almost cloudy-looking).
The fish love playing in the bubbles, and I love the look of it in the tank.
I didn't buy the airstone/pump with an increased oxygenation in mind, so if it makes the water even better for the fish that's a bonus.

 

[TribeOfShroom]

I'm unable to add any scientific answers or evidence either way, but since I put in a new bubble wall (the correct size for my air pump) I've noticed that there is a hell of a lot more general flow around the tank, the water surface is being aggitated more and my water clarity has become superb!

Without scientific evidence, I'm going to sound silly. But I think the clarity has something to do with there being more oxygen in the water for the bacteria within my two internal filters to process.

 

[steelhealr]

Add to this...the airstone really functions NOT by adding bubbles to the tank but by creating an upward movement of water from the bottom of the tank. You could argue that although a powerhead agitates more surface water which is probably at an already HIGHER level of water saturation, the airstone moves a GREATER VOLUME OF LOWER SATURATED WATER to the surface, thus reoxygenating better. There is no correct answer to this but I think that CFC's method...is probably the best way:
-high disturbance at the surface
-recycle bottom water to the top.

SH

 

[Nim]

Thats a very interesting thread and both sound pretty good.. However for biggeners who often tend to buy toy pumps from fish stores, it really would the the powerhead that will areate the water more then the airpump.

Nevertheless, very interesting.

Nim

 

[Spider Pig]

I would argue that an air pump would theoretically create more oxygenation, as the many small bubbles provide a greater surface area for diffusion than surface agitation alone, and so there is greater ability for atmospheric oxygen to dissolve in the water.

The oxygen saturation at the bottom of the aquarium is likely to be lower than that at the top of the aquarium (assuming that the air stone is at the bottom) as the top is in contact with the atmosphere and so there will be a diffusion gradient throughout the tank from top to bottom (which will of course be affected by circulation) Therefore the gradient between atmospheric oxygen from the air pump and dissolved oxygen in the water will be greater and so more diffusion of oxygen to the water will occur than at the surface where there is (theoretically) a shallower diffusion gradient. Assumption here that both powerhead and air pump create circulation.

All this is relatively theoretical as it is likely that the water is pretty saturated anyway. To test you would also have to specify what size airpump vs powerhead. Angle of powerhead and so agitation caused (fountain or mere rippling) lots of variables- but size for size i'd guestimate air pump.

 

[waterdrop]

I thought I remembered that bignose or someone had argued in another thread that bubble surface area was insignificant (for some reason) compared to top surface area.

 

[Colin_T]

One thing you could do is use a water pump/ powerhead with an air attachment or venturi. Then you get the best of both worlds

And just to add another factor into this equation. If you have a really tight fitting coverglass over the entire top of the tank, you will only have a small area for the air above the aquarium water to get replaced by the air in the room. This can reduce the amount of oxygen getting into the water. By having an airpump blowing air into the tank, you will be getting (theoretically) a fresher source of air with potentially more oxygen in it.

And all the surface turbulence removes excess CO2 which the plants use during the day. Oh No, what do we do now

 

[Spider Pig]

I thought I remembered that bignose or someone had argued in another thread that bubble surface area was insignificant (for some reason) compared to top surface area.

quite surprised. Did the math. guestimate average bubble 1mm radius, gives surface area of 0.1256 cm2. Average 18"x12" aquarium has surface area of 1393.54cm2. Therefore you need about 11000 bubbles to equal this area. Although there are a lot of bubbles given off, I'm sure its not near this amount, although it may be possible with a long airstone.

Another factor, probably insignificant, that air introduced under pressure to the bottom of the aquarium should diffuse more oxygen into the water than air at atmospheric pressure at the surface of the aquarium. Too many variables to know what affect this has directly.

 

[waterdrop]

I thought I remembered that bignose or someone had argued in another thread that bubble surface area was insignificant (for some reason) compared to top surface area.

<...>
Another factor, probably insignificant, that air introduced under pressure to the bottom of the aquarium should diffuse more oxygen into the water than air at atmospheric pressure at the surface of the aquarium. Too many variables to know what affect this has directly.

Yes, probably insignificant again for this one, I seem to recall (and must warn I might be making this up in my mind) that the introduction of the bubble at the bottom and then its movement to the top all takes place too quickly for the added pressure to amount to any significant increase in diffusion.

~~waterdrop~~