[BigAl07]

Foam Fractionation (Protein Skimmer process) only works "well" in salt water. Fresh water isn't dense enough and the Dissolved Organic Compounds can't get separated. You'd be merely using it as a large volume "Air Stone" and wasting a lot of energy with little to no benefit.

You can use a Protein Skimmer in a freshwater aquarium. A skimmer will not hurt the freshwater fish or degrade the water quality, and the freshwater will not damage the skimmer.

Ironically the term Protein Skimmer is a false one or at least not entirely accurate any more. It was at one time thought that Protein Skimmers only removed large molecules of protein from the tank but it's now known they remove many more than just protein which is why we use them so heavily in our reef tanks.