Skim wet or dry?

I think this article should just be stickied here in the skimmer section.

What is Skimming? by Randy Holmes-Farley - Reefkeeping.com

Foam Formation and Draining
Once a skimmer contains a large number of bubbles coated with organics, it is necessary to somehow remove the bubble surfaces, but not the majority of the water nearby. This is most easily accomplished by allowing the bubbles to form a foam. Foam formation takes place when bubbles accumulate and interact. The froth of bubbles begins to drain under gravity, removing much of the water between the bubbles. Some of the bubbles merge into larger bubbles. As long as the bubbles do not pop before significant draining occurs, then the organics will be left behind in the foam, along with some residual water. Eventually, the concentration of organics on the top of the foam becomes great enough that they exceed the solubility limit, and small particulates of organics form. These particulates are generally what a skimmer collects, along with some water and organics that remain present in solution or at the air/water interface.

Wet vs. Dry Skimming
Foam draining is a critical stage for most skimmers. One problem with drainage is that some organics are washed away with the draining water. There is always an equilibrium between organics in solution, and those actually attached to the interface. As water continues to drain, some of the organics are lost. Further, as some bubbles pop and their organics are redistributed into the nearby water, the local concentration of organics in the water between the bubbles in the foam can rise to concentrations far higher than are present in the aquarium. For this reason, the most effective skimming, in terms of total organic removal, comes from removing somewhat wet foam, rather than waiting for this same wet foam to drain prior to removal. The primary difference between wet foam, and drained dry foam, is that additional water and some organics have drained away. A dry form is more efficient in terms of the amount of organic removed in relation to the water volume, and all skimmers and their potential adjustments strike some balance between removing more water and slightly more organics, or less water and slightly fewer organics. Perhaps a careful analysis of different types of skimming will, in the future, show this expected result experimentally.


I try and stay in the middle.