Skimming is a physical procedure for depuration, for removal of certain substances from water. During this process it is not at all needed to distinguish between useful or dangerous substances, so much so that water not only loses those that affect the organic load, but also many mineral elements of vital importance to the aquarium’s inhabitants, in a very similar way to what happens with active carbon, which usually works in a non selective way. Besides, skimming also increments gas exchange in the aquarium. Gasses present in the aquarium in excessive quantities, a further increase of which could be dangerous, are expelled while oxygen is mixed with the water. All of this happens in a passive manner by means of the huge contact surface that forms in the confine area between air and water, in other words on the surface of air bubbles. With the skimmer then there is a relevant increase in the aquarium’s water surface.
“Friction” between air and water
A physical condition for skimming is the movement of those tiny air bubbles in the water. Through this movement a certain “attrition” between air and water is generated, modifying the electric potential of air bubbles and storing certain substances present in the water. It is, in particular, carbohydrates, but since these have the property of being able to bind several diluted substances to them, in a way they act as a “vehicle” for other compounds. This storing leads to the fact that air bubbles involved in the process do not burst, instead being compressed upwards in a collection “glass”, by air pushing from downside, to finally being removed from water circulation. The advantage of skimming is evident: water is deprived from polluting organic substances, in order to make the presence of more metabolically active animals possible and, in this case, feed them more abundantly. Many delicate fishes are almost not sustainable in aquarium without the presence of a skimmer. A lot of corals too, living in the sea in extremely pure waters, are more effectively sustainable long term with the use of a skimmer.
Competition for filter feeders
However, skimming also has disadvantages, since it removes from the water substances of vital importance. Of course the mineral ones, like oligo elements (trace elements), can easily be reintegrated with concentrates easily available on the market, but the skimmer also removes substances that serve to feeding as nutritional staples to many animals. In a certain way the skimmer represents competition for filtering animals, a technical “diner”. Tube worms, sponges and other filtering animals are usually harder to keep in good health the more efficiently the skimmer works. For this particular reason a strong and efficient skimming in the aquarium equals to some sort of walk on the razor’s edge. We create conditions that are poor in nutritional substances, which are very important for the maintenance of fishes and corals with a symbiotic life, and at the same time we complicate the existence of filtrators. So those who want to assemble a community aquarium rich in metabolically active fishes, and in this particular case also maintaining sensible hard corals, will need the best quality of water, in this case the use of a skimmer is well recommended. For a common aquarium this piece of equipment reveals itself as extremely useful. For those instead who would like to assemble a thematic tank, one made to nurture filter feeder organisms in the best possible way, a skimmer would be counterproductive.