Why does salt water make fine bubbles in the skimmer?

[Ocelaris]

Someone posted a thread about their skimmer only making big bubbles, and I noticed he was using freshwater. My experience is that freshwater only makes big bubbles and saltwater makes really fine bubbles. So my question is why?

I think it has to do with the dissolved ions attracting air better, but not sure why? I know this has to do with why we don't use Skimmers on freshwater tanks except if there is ozone; so I know it has something to do with oxidation potential, but can't put my finger on it?

Hopefully this is a fun question and not a repeat!

 

[Reef man 89]

Following along I am pretty curious of this myself.

 

[Ocelaris]

There are so many explanations of why proteins bond to air (hydrophobic/hydrophilic) and that more bubbles = more surface to trap protiens etc... But everyone skips over the fact that in a zero nutrient system salt water still makes smaller bubbles than fresh water.

I can't ever recall why a chemical difference allows the physical size to be smaller. But I'm guessing it has to do with the surface tension of the nitrogen/oxygen in the water wanting to stick together more in fresh water. Where as in salt water the dissolved ions make the individual ions more attracted to the water? Since Ozone has a high oxidizing potential i.e. to stick to other molecules and that has fine bubbles (I assume), then the ionic attraction of the molecules in water must have something to do with the size... I'm just jumping around the real answer, but hopefully clarifies what I'm looking for.

Here's the thread where this guy was having the issue:

https://www.reef2reef.com/threads/help-ro-dc-3500s.301254/

 

[@drian]

Thank you for trying to help me with this case.
During these days I'm going to test with salt water!
I am also investigating why in salt water microbubbles are generated and not fresh water.
I even thought about selling the Skimmer

Thank you

 

[Randy Holmes-Farley Verified Community Expert]

I address this question here:

What is Skimming? by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2006-08/rhf/index.php

from it:

1. Why does skimming work better in saltwater than in freshwater?

There are two fundamental reasons that skimming is more effective in seawater than in freshwater. One is the reduced solubility of organics, especially hydrophobic ones. Because many organics are less soluble in saltwater than in fresh, they are more easily squeezed out of it to an air/water interface, and collected as foam. This is the basis for the well-known salting-out effect of proteins. Quoting from a basic biochemistry text: "At sufficiently high ionic strength a protein may be almost completely precipitated from solution, an effect called salting-out."

A second reason for less efficient skimming of freshwater relates to bubble formation and coalescence. It turns out that air bubbled into seawater forms smaller bubbles than if the same device bubbled into freshwater.1-4 The possible reasons for this have been discussed in the scientific literature, but the exact reason is not universally agreed upon.

Despite the fact that skimmers usually produce larger bubbles in freshwater, and that organics are often more soluble in freshwater, it is not impossible to skim freshwater. Rivers from certain areas of the northeastern United States sometimes have foam on them, which comes from tree sap and other natural organics that enter the water. They have a low solubility in water, and are easily collected as foam in a natural skimming action.

General References:

1. Bubble shattering: differences in bubble formation in freshwater and seawater. Slauenwhite, David E.; Johnson, Bruce D. Department of Oceanography, Dalhousie University, Halifax, NS, Can. Journal of Geophysical Research, [Oceans] (1999), 104(C2), 3265-3275.

2. Bubble-size distributions produced by wall injection of air into flowing freshwater, saltwater and surfactant solutions. Winkel, Eric S.; Ceccio, Steven L.; Dowling, David R.; Perlin, Marc. Mechanical Engineering, University of Michigan, Ann Arbor, MI, USA. Experiments in Fluids (2004), 37(6), 802-810.

3. Laboratory air bubble generation of various size distributions. Puleo, Jack A.; Johnson, Rex V.; Kooney, Tim N. Marine Geosciences Division, Naval Research Laboratory, Stennis Space Center, MS, USA. Review of Scientific Instruments (2004), 75(11), 4558-4563.

4. Bubble size in aerated stirred tanks. Alves, S. S.; Maia, C. I.; Vasconcelos, J. M. T.; Serralheiro, A. J. Department of Chemical Engineering, Centro de Engineering Biologica e Quimica, Instituto Superior Tecnico, Lisbon, Port. Chemical Engineering Journal (Amsterdam, Netherlands) (2002), 89(1-3), 109-117.

 

[Ocelaris]

Thank you!

 

[@drian]

I address this question here:

What is Skimming? by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2006-08/rhf/index.php

from it:

1. Why does skimming work better in saltwater than in freshwater?

There are two fundamental reasons that skimming is more effective in seawater than in freshwater. One is the reduced solubility of organics, especially hydrophobic ones. Because many organics are less soluble in saltwater than in fresh, they are more easily squeezed out of it to an air/water interface, and collected as foam. This is the basis for the well-known salting-out effect of proteins. Quoting from a basic biochemistry text: "At sufficiently high ionic strength a protein may be almost completely precipitated from solution, an effect called salting-out."

A second reason for less efficient skimming of freshwater relates to bubble formation and coalescence. It turns out that air bubbled into seawater forms smaller bubbles than if the same device bubbled into freshwater.1-4 The possible reasons for this have been discussed in the scientific literature, but the exact reason is not universally agreed upon.

Despite the fact that skimmers usually produce larger bubbles in freshwater, and that organics are often more soluble in freshwater, it is not impossible to skim freshwater. Rivers from certain areas of the northeastern United States sometimes have foam on them, which comes from tree sap and other natural organics that enter the water. They have a low solubility in water, and are easily collected as foam in a natural skimming action.

General References:

1. Bubble shattering: differences in bubble formation in freshwater and seawater. Slauenwhite, David E.; Johnson, Bruce D. Department of Oceanography, Dalhousie University, Halifax, NS, Can. Journal of Geophysical Research, [Oceans] (1999), 104(C2), 3265-3275.

2. Bubble-size distributions produced by wall injection of air into flowing freshwater, saltwater and surfactant solutions. Winkel, Eric S.; Ceccio, Steven L.; Dowling, David R.; Perlin, Marc. Mechanical Engineering, University of Michigan, Ann Arbor, MI, USA. Experiments in Fluids (2004), 37(6), 802-810.

3. Laboratory air bubble generation of various size distributions. Puleo, Jack A.; Johnson, Rex V.; Kooney, Tim N. Marine Geosciences Division, Naval Research Laboratory, Stennis Space Center, MS, USA. Review of Scientific Instruments (2004), 75(11), 4558-4563.

4. Bubble size in aerated stirred tanks. Alves, S. S.; Maia, C. I.; Vasconcelos, J. M. T.; Serralheiro, A. J. Department of Chemical Engineering, Centro de Engineering Biologica e Quimica, Instituto Superior Tecnico, Lisbon, Port. Chemical Engineering Journal (Amsterdam, Netherlands) (2002), 89(1-3), 109-117.

Excellent friend, thank you very much!
Something I could read, is that the foam lasts more depending on the temperature of the water.

 

[Randy Holmes-Farley Verified Community Expert]

You're welcome

Happy Reefing.

 

[@drian]

Many thanks Ocellaris and Randy, yesterday I tried it in salt water and this works perfectly
That was the solution