Foaming Properties of Salt Water

[gabew]

So the other day I got this protein skimmer second hand for my new tank. I spent $100 on it so I was hoping it was pretty good. I brought it home and decided to test it in a bucket of fresh water to make sure it worked, and just what is was bull ****! It bubble forming was horrible instead of a nice cloud of bubbles it was about as bubbly as your average air pump with no air stone.
I was really ****ed off so I tried everything I could to get it to work. Finally I has an idea :idea: maybe if I added some salt, you know because you see so much nice foam on the beach i thought it wouldn't hurt.
So I added enough basic table salt to get it about at the salinity of salt water and, boom, the simmer worked perfectly. It was making a nice clout of tiny bubbles and it quickly started forming a layer of gunk. :celeb1:
So my question is, Why exactly is salt water so much more bubbly than fresh?

 

[HighlandReefer]

What is Skimming?
http://reefkeeping.com/issues/2006-08/rhf/index.php

From it:

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.