We’ve all seen foam on the beach or river banks and this is a natural phenomenon exploited by the technique of ‘Foam Fractionation’. This exploits a property of organic compounds (here comes the science bit...) which have both Hydrophobic and Hydrophilic elements. In simple terms they’re attracted to an interface between air and water such as an air bubble or the water’s surface.
A protein skimmer is a device that brings aquarium water into contact with a large concentration of air bubbles and although most efficient in denser, salt water they can also be used in some freshwater systems such as koi ponds. Standard components of a skimmer include air injection (via air pumps in older models or venturi intakes in more modern units) a contact chamber and a collection cup where foam accumulates and can be removed.
As this process removes organic pollutants before being broken down by bacteria, it has the effect of lowering waste levels and can be made even more efficient by using ozone. By effectively short-circuiting the normal oxidisation of waste it slows the accumulation of nitrates and phosphates which can have many benefits.