Surface tension

[Graham Ramsay]

Can anybody help my comprehension with this please?
Many web sites (and a few answers in newsgroups) say
that using an airstone will break the surface tension
(which it surely will) and thus increase the exchange of
gas. Almost as if the surface tension was preventing
the gas from moving between water and atmosphere.
In a forum I'm in I received this response when I claimed
that a circular water current and surface agitation,
not the breaking of surface tension or the increased
contact area due to air bubbles, was the main purpose
of using an airstone:

Quote:
"Surface tension is needed to stop complete gaseous escape
from a body of water. breaking up the surface tension promotes
far greater gaseous exchange"
Unquote:

Now I left school some time ago and never went to
college but it strikes me that if that were true then, by
the simple act of adding a drop of detergent to the water
surface, all the gas in the water would now escape into
the atmosphere.
How does surface tension, on its own, prevent the exchange
of gas between a body of water and the atmosphere?

Thanks for your time.

--
Graham Ramsay

[Roger Sleet]

In article >,
(Graham Ramsay) wrote:

> Can anybody help my comprehension with this please?
> Many web sites (and a few answers in newsgroups) say
> that using an airstone will break the surface tension
> (which it surely will) and thus increase the exchange of
> gas. Almost as if the surface tension was preventing
> the gas from moving between water and atmosphere.
> In a forum I'm in I received this response when I claimed
> that a circular water current and surface agitation,
> not the breaking of surface tension or the increased
> contact area due to air bubbles, was the main purpose
> of using an airstone:
>
> Quote:
> "Surface tension is needed to stop complete gaseous escape
> from a body of water. breaking up the surface tension promotes
> far greater gaseous exchange"
> Unquote:
>
> Now I left school some time ago and never went to
> college but it strikes me that if that were true then, by
> the simple act of adding a drop of detergent to the water
> surface, all the gas in the water would now escape into
> the atmosphere.
> How does surface tension, on its own, prevent the exchange
> of gas between a body of water and the atmosphere?

This is rubbish. Bubble do not break the surface tension, bubbles are
little balls of surface tension. It sounds like someone has taken a quite
long explanation of why the gaseous exchange takes place, and simplified
it to the point where it is no longer true. The truth is all about rates
of delusion and fluid dynamics, which are far too complicated to go into
here - and anyway I'd have to go and look them up.

Roger Sleet
Roger's Aquatic Pages http://www.sleet.plus.com

[Graham Ramsay]

>"Roger Sleet" wrote
>
> This is rubbish. Bubble do not break the surface tension, bubbles are
> little balls of surface tension. It sounds like someone has taken a quite
> long explanation of why the gaseous exchange takes place, and simplified
> it to the point where it is no longer true. The truth is all about rates
> of delusion and fluid dynamics, which are far too complicated to go into
> here - and anyway I'd have to go and look them up.

Thank you Roger, I suspected that was the case.

--
Graham Ramsay

[Jeff Dantzler]

Bubbles promote gas exchange because they create water movement
at the surface. Surface tension has nothing to do with it.

Jeff Dantzler

[Marc Klein]

Can you tell what helps to break the tension?

"Jeff Dantzler" > schreef in bericht
news:1064429532.327025@yasure...
> Bubbles promote gas exchange because they create water movement
> at the surface. Surface tension has nothing to do with it.
>
> Jeff Dantzler

[Bob K.]

>Can you tell what helps to break the tension?
>
>"Jeff Dantzler" > schreef in bericht
>news:1064429532.327025@yasure...
>> Bubbles promote gas exchange because they create water movement
>> at the surface. Surface tension has nothing to do with it.

? A beer?

[Charlie Spitzer]

soap

why are you concerned about surface tension in the first place?

"Marc Klein" > wrote in message
...
> Can you tell what helps to break the tension?
>
> "Jeff Dantzler" > schreef in bericht
> news:1064429532.327025@yasure...
> > Bubbles promote gas exchange because they create water movement
> > at the surface. Surface tension has nothing to do with it.
> >
> > Jeff Dantzler
>
>

[Jeff Dantzler]

Charlie Spitzer > wrote:
> soap

> why are you concerned about surface tension in the first place?


Charlie's right. In a freshwater aquarium, the only way you will
deviate from "normal" surface tension is by adding a surfactant like
soap or dawn or laundry detergent etc. But then your fish will be
injured or dying...

Surface tension does not play a role in oxygenation.

Oxygen gets into your tank primarily by diffusing into the water
at the surface. If the water is still, the layer at the surface gets
more saturated with oxygen, but the lower depths can become oxygen
defficient. That is why water movement is important. It is the
water movement caused by bubbles (from an airstone) that promotes
oxygenation and not the bubbles. They are small and have very little
oxygen in them compared to the rest of the atmosphere that interacts
with the surface of your water comlumn.

In overstocked tanks when the power goes out and there is no pump
or filter or airstone to circulate the water, fish can suffocate
to death because they will use up the dissolved oxygen faster than
it can diffuse into the tank.

On the other hand, if you run a sump/trickle tower arrangement,
you will never have to worry about low oxygenation because
the large surface area of the biomedia promotes very efficient
gas exchange.

See: http://cichlidae.com/articles/a014.html

JLD