Function Of A Protein Skimmer
Skimming removes certain organic compounds from your aquarium water, including proteins and amino acids, by using the polarityof the protein itself. Due to their intrinsic charge, water-borne proteins are attracted to the air/water interface. This units work by injecting numerous tiny bubbles into the water column. The small bubbles present an enormous air/water interface for the protein molecules to cling to. The longer the bubble resides in the water, the more proteins it is able to attract. The action of a protein skimmer is often compared to the action of waves producing sea foam.
The term protein skimming is misleading because this form of filtration removes other substances besides proteins. These other substances include fats and fatty acids, carbohydrates, metals such as copper complexed with proteins, and certain trace elements such as iodine, in addition to particulates and other detritus, phytoplankton and bacteria.
Design
The basic units design consists of a main chamber through which aquarium water flows. Air is injected into the column as fine bubbles. The surface of the bubbles collect proteins and other substances and carries them to the top of the device where a collection cup allows the foam to leave the main chamber. Here the foam condenses to a liquid, which is removed from the system. This material can range in color from a light tea to black tar.
Every skimmer operates either by co-current flow, in which the water flows upward in the column along with the bubbles, or by counter-current flow, in which the water flows downward against the direction of the bubbles. Counter-current skimmers are more efficient because of the greater contact time the water has with the bubbles.
Air Stone Driven
The original method of protein skimming, it is not completely obsolete, although many newer technologies have eclipsed this method. The air stone is a ceramic block with an air hose attached that runs to a small air pump. The stone is placed at the bottom of a tall column of water. The tank water is pumped into the column, allowed to pass by the rising bubbles, and back into the tank. To get enough contact time with the bubble, these units can be many feet in height. While this method has been around for many years, many regard it as inefficient for larger systems or systems with large bio-loads.
Downdraft Design
Pumped tank water enters through a small vertical column next to the main column, that contains a plastic media that shreds the water, entrapping air in to the stream. The result is a milky white appearance of very fine bubbles. The stream enters a mixing box and is allowed to rise within the reaction chamber. This is one of the current top skimming methods due to its compact size and high efficiency.
Venturi Operated
The premise behind these units is that a venturi valve can be used to introduce the bubbles into the water stream. The tank water is pumped through the venturi, in which fine bubbles are introduced, then enters the skimmer body. This method is popular due to its compact size and high efficiency.
A new variation on the venturi is the needle wheel(tm). This method of bubble generation evolves from another method that uses a turbine within the water stream to create bubbles. Essentially this method uses a pump to pull water past a venturi - before the pump - then past the pump's impeller which smashes the bubbles into very fine bubbles, and into the skimmer column.
Spray Induction
This method is related to the downdraft, but uses a pump to power a spray nozzle, fixed a few inches above the water level. The spray action entraps and shreds the air in the base of the unit, which then rises to the collection chamber.
