Studies of Wet vs Dry Skimming

[pjf]

There are 3 theories about wet versus dry skimming:

1. Per Anthony Calfo, there is a compositional difference between wet and dry skimming. Wet skimming removes more particulate matter. Dry skimming removes more dissolved organic compounds (DOC).

2. A second theory is that wet and dry skimming differs only in the amount of moisture collected.

3. A third theory is that while wet skimming collects more moisture, it removes more particulates and DOC’s than dry skimming. Dry skimming comes at the expense of letting some particulates and DOC’s escape back into the water column.

Are there any studies to support any of the above theories?

Thanks!

[Roland Jacques]

Good question, I go with theory #3.

Id say the Chemistry fourm may be a verygood place to also post this question. and even over on the Zeovite web site.

I got to say that kind of suprising coming from Calfo. are you sure if was not comparing NW foam (dryer) to beckett foam (Wetter)?

[JC VT]

Another vote for #3.

Here's a quote from KathyL who posted in Borneman's thread on skimmate:




I have an unusual system in that I breed clownfish. So my tanks are fish only. I feed heavily 3-5 times a day, and I have about 1000 juvenile clownfish in about 160 gallons.

...

Then I tested system water, in the order of how it circulates in the system:
Water skimmed from the surface of fish tanks: 5 ppm nitrate
Dripping out of bioball trickle filter: 5 ppm
taken from the surface of the sump: 5 ppm
After the PURA filter: 5 ppm
After the UV filter: 5 ppm

Either the test kit is just wrong, or my daily practice of removing detritus is very effective in keeping nitrates in check. I am surprised that there are not more nitrates in the sump surface water at the least. I am surprised there are not more nitrates in the trickle water, too. My husbandry removes only the solid matter daily.




This is a very good argument for wet skimming to get particulates out.

[pjf]

I first heard Anthony Calfo explain the compositional difference between wet and dry skimming on “reef video� (http://www.reefvideos.com/). You can hear it 15 minutes into the podcast, called “Anthony Calfo Video 2.�

I’m not sure why Calfo thinks there is a difference in the composition of wet and dry skimmate. Perhaps he thinks that large “wet� bubbles are adept at removing particulates and small “dry� bubbles have longer contact time with DOC's. (My words, not Calfo’s.)

[JC VT]

A clean bubble with more exposed surface area would logically have greater absorption of DOC than a dirty bubble. Bubble size has little to do with wet or dry skimming; the same skimmer with same size bubbles can be dialed to have either wet or dry foam.

Wet skimming particulates should get compounds before they become dissolved anyways.

[pjf]

When you dial more air, does that not also create larger bubbles? I'm under the impression that large bubbles rise more quickly and therefore have less contact time with DOC's than smaller bubbles.

[JC VT]

Regardless of wet or dry skimming the goal is small bubbles to increase the air/water interface per unit of air.

Randy does not believe contact time is critical to protein skimming.

So the point then would be simply to have more interfacial area available (via smaller bubbles), rather than stagnating bubbles. If people saw the greatest protein skimming from smaller bubbles, then it likely came from the increased interface area, not contact time.

[pjf]

Thanks for mentioning Randy Holmes-Farley. In one of his articles, I see that he seems to favor wet skimming (theory #3):

"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."
(http://reefkeeping.com/issues/2006-08/rhf/index.php)

[Slamajama]

foam,foam,foam...