Protein skimming, or “foam fractionation,” ranks among the most valuable techniques available for maintaining a successful marine aquarium. Although numerous designs exist, from nano protein skimmer units for desktop-size aquariums to units large enough for a 300-gallon tank, the operating principle is the same.

Water from the aquarium is directed into the protein skimmer via a pump. The skimmer consists of a tall columnar tube with a collecting cup mounted at the top. Air is pumped in at the bottom of the column, either via a separate air diffuser, or via a Venturi on the water pump line. Airflow is adjusted to maintain a mass of foam at the top of the column. The foam is produced as molecules and tiny particles of organic matter coalesce on the surface of the air bubbles. When the foam layer is large enough, it spills over into the collecting cup, from which it can be discarded. The material in the collection cup is referred to as “skimmate.”

To maximize contact time between the aquarium water and the air bubbles, some skimmers pump water from the top of the column downward, creating a countercurrent as air bubbles rise toward the surface.

While some aquarists maintain that skimming removes iodine, and perhaps other valuable ions, from the water, these are easily replenished via water changes and the use of additives. The value of skimming to remove excess organic matter cannot be overestimated.

Different marine organisms react differently to the presence of dissolved organic matter. Most fish can me maintained successfully without using a skimmer on the aquarium. However, delicate stony corals generally cannot tolerate significant amounts of dissolved organics, and therefore a skimmer is required on most reef tanks.

The primary advantage of protein skimming is the physical removal of organic matter from the system. Mechanical filtration media trap particles, but if the medium is not cleaned or changed frequently, the particles break down and contribute to waste build-up in the aquarium. Similarly, chemical filtration media trap organic molecules, but the medium remains in contact with the aquarium water as trapped molecules are broken down by bacteria.

Secondary advantages of skimming include:

  • reduction of nitrate and phosphate levels
  • elimination of toxic secretions from aquarium inhabitants
  • promotes oxygenation
  • eliminates carbon dioxide
  • prevents surface film accumulation, which reduces light penetration

Skimming is a unique, essential method for reducing dissolved organic matter in the marine aquarium