Purpose of Protein Skimmers

The oceans on our planet skim proteins naturally by churning along the seashore, creating sea foam that blows onto the beach. What is in this brownish-yellow scum? Animal waste products from the fish, invertebrates, mammals and anyone else out in the ocean. Churning against rocky shores creates air bubbles under the surface that bring organic compounds with them to shore. This process is also known as "foam fractioning." A saltwater aquarium is a miniature ocean, and the creatures within it create the same organic waste compounds. A protein skimmer is an artificial method of foam fractioning used to clean the water.

  1. The Facts

    • All living creatures in the tank produce waste products such as ammonia compounds and phenol oils, which can create a yellow tint to the water. Dissolved organic compounds often have two parts: a water-loving (hydrophilic) part and a water-repelling (hydrophobic) part. The hydrophobic part wants to be in the air and so the compounds float near the surface; these are called "surfactants." When air is passed through these surfactants, bubbles form (because the hydrophobic part has found air) and the bubble carries the surfactant skin to the surface. Along the way, these skinned bubbles pick up other compounds in the water and carry them upward. With enough bubbles, a foam of waste material is created.

    History

    • Municipal waste treatment plants discovered foam fractionation brought scum to the surface and left the remaining liquid much cleaner. Protein skimmers have been used by saltwater aquarists since the 1970s.

    Function

    • Protein skimmers are used by saltwater aquarists to remove excess organic waste products from the water before they can transform into chemicals toxic to the living inhabitants and mechanical systems of the tank. Water is pumped into a separate reaction chamber where the bubbles are run in a column; smaller, more numerous bubbles are more efficient because of the increase in surface area. The foam that floats to the top must be skimmed off or it will dissolve back into solution and remain in the water. Proteins skimmed off the top are pushed into a collection cup or jar to be disposed of. The skimmed water, now cleaner, is returned to the tank, sometimes via a sump.

    Types

    • A co-current skimmer is the simplest variety of protein skimmer, with an open-bottomed, in-tank reaction chamber (or in-sump) and a bubbling device, such as an air stone, at the bottom. This method is passive, because the water comes in and out of the bubble chamber on its own, with no pumping.
      Counter-current skimmers actively pump water in through the top of the reaction chamber aimed downward, running counter to the current of bubbles in an enclosed reaction chamber. This increases the length of time material is suspended in the bubble column, leading to greater efficiency. Counter-current skimmers can either hang on the back of the aquarium or be sump-mounted.
      Venturi-style skimmers use a Mazzei valve, which restricts the water flow and adds air so that water enters the reaction chamber already foamy. The angle of the valve creates a vortex within the reaction chamber, further stirring the water in the protein skimmer.
      The "Environmental Tower Skimmer" (ETS) or downdraft skimmer is a more recent innovation. Water from the aquarium is run through a column of beads known as "bioballs" which break up the water and add air, creating a foam by the time the water reaches the bottom. The foam and water are pushed into a container where a baffle protects the return-pipe to the aquarium and the foam floats to a collection chamber.

    Size

    • A larger aquarium will need a larger-volume protein skimmer. A co-current skimmer is adequate for tanks smaller than 40 gallons. Fish and reef keepers would do best with a reaction chamber no smaller than 4 inches wide by 6 inches tall for a 20 gallon tank. For tanks over 100 gallons, skimmers with reaction chambers up to 24 inches tall by 6 inches in diameter can be purchased from commercial aquarium supply outlets. Homemade protein skimmers can, of course, vary in dimensions. See Resources for choosing the best size for your saltwater aquarium.