. While this method has been around for many years, many regard it as inefficient for larger systems or systems with large bio-loads. Venturi The premise behind these skimmers is that a venturi pump, or aspirator, 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 was popular due to its compact size and high efficiency but venturi designs are now more likely to be included in other skimmer designs rather than as a simple venturi design. Counter-current flow systems Aspirating: pin-wheel/adrian-wheel, needle-wheel, mesh-wheel This basic concept is more correctly known as an aspirating skimmer, since some skimmer designs using an aspirator do not use a "Pin-Wheel"/"Adrian-Wheel" or "Needle-Wheel". "Pin-Wheel"/"Adrian-Wheel" describes the look of an impeller that consists of a disk with pins mounted perpendicular (90°) to the disc and parallel to the rotor. "Needle-Wheel" describes the look of an impeller that consists of a series of pins projecting out perpendicular to the rotor from a central axis. "Mesh-Wheel" describes the look of an impeller that consists of a mesh material attached to a plate or central axis on the rotor. The purpose of these modified impellers is to chop or shred the air that is introduced via a venturi apparatus or external air pump into very fine bubbles. The Mesh-Wheel design is fairly new and, while providing excellent results in the short term because of its ability to draw in more air and create finer bubbles with its thin cutting surfaces, it is still being developed and will likely continue to evolve over a few more years. This style of protein skimmer has become very popular and is believed to be the most popular type of skimmer used with residential reef aquariums today. It has been particularly successful in smaller aquariums due to its usually compact size, ease of set up and use, and quiet operation. Since the pump is pushing a mixture of air and water, the power required to turn the rotor can be decreased and may result in a lower power requirement for that pump vs. the same pump with a different impeller when it is only pumping water. Downdraft The Downdraft skimmer is both a proprietary skimmer design and a style of protein skimmer that injects water under high pressure into tubes that