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View Full Version : can u use a skimmer for freshwater tanks?


timdam
02/03/2010, 10:50 PM
Not sure what forum i should ask this. but doesn't a skimmer help to remove all that fish crap. if so, why don't people use it for freshwater tanks?

swjim
02/03/2010, 10:53 PM
Nope. No salt -no skim.

syrinx
02/03/2010, 10:55 PM
Fresh water doesnt produce a good foam, so it is not used indoors on fresh tanks. We do install them in Koi ponds sometimes- but the design is much diffrent than the standard applications.

Randy Holmes-Farley
02/04/2010, 08:21 AM
Salt has a couple of important properties that relate both to bubble formation (not especially well understood) and the solubility of organics (well understood) that reduce its effectiveness substantially in fresh water.

I discuss it here:

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


from it:

http://reefkeeping.com/issues/2006-08/rhf/index.php#6a

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.