Better Water Flow, More Effective Mixing, and Longer Contact Time. Water enters at the top of the skimmer and is drawn downward, using the full length and diameter of the Contact Chamber. When the bubbles produced by the air diffuser travel upward against the downward water flow, a spiraling turbulence is created. The turbulence causes air bubbles and water to mix for an extended period of time. This allows organics to be extracted more efficiently. Contact time is also increased by using the tallest Protein Skimmer that your aquarium will accommodate.