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To Skim or Not to Skim?

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Some recent articles in Advanced Aquarist by Ken Feldman et al have looked at the performance of skimmers and the constituents of skimmate.

There are some surprising results. In a nutshell, skimmers are only capable of removing about 25% of total organic carbon. That may be due to many compounds not being attracted to the air/water interface. It also turns out that skimmate is, surprisingly, made up largely of inorganic compounds. That may mean that skimmers are mostly removing microorganisms such as diatoms, not free organic molecules.

http://www.advancedaquarist.com/2010/2/aafeature
http://www.advancedaquarist.com/2010/1/aafeature
http://www.advancedaquarist.com/2009/1/aafeature2

This is all making me wonder if a skimmer really provides much benefit. It seems like if there are organic compounds that really need to be removed, something like GAC will likely be necessary since a skimmer only removes a small percentage of them. Skimmers may help with nutrient control because they remove microorganisms, but growing and harvesting macroalgae may be just as (or possibly more) effective at that. So if you're running carbon and growing chaeto, does a skimmer really provide any benefit?

I'm curious to hear opinions on this. Also, if you've tried running your tank both with and without a skimmer, what differences did you see?
 
one thing which immediately comes up is the identity of what IS removed. Amounts only matter if all things are equal. If the skimmer only removes 25%, but it removes the bad 25% which cause detriment to the tank, then we have a totally different argument.
 
I just read through the first article. I think a lot of assumptions are made, some probably poor. I don't like how he assumes that all calcium/mag is inorganically bound. How can you say that this calcium/magnesium wasn't organically bound in the cell wall of an algae cell. I think he discounts a lot of that so the percentage of organic material pulled really should be much higher.
 
Ian, I think you have a different picture of "organic bound". Organic bound, means that it is the metal center or ligand of an organic complex. Our bones for example aren't organic bound, but the iron in our hemoglobin is.
 
Well you might say why do water changes at all too, if you do 15% you're only removing 15% of the (whatever).... but that 15% can make all the difference in the world. I suspect even if the authors methods weren't flawed removing 25% of TOCs vs not removing any would do all the wonder in the world.
 
sfsuphysics said:
Well you might say why do water changes at all too, if you do 15% you're only removing 15% of the (whatever).... but that 15% can make all the difference in the world. I suspect even if the authors methods weren't flawed removing 25% of TOCs vs not removing any would do all the wonder in the world.
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+1.

It might be only 25%, but in addition to the water changes, and the collective whole it makes a difference.
 
sfsuphysics said:
Well you might say why do water changes at all too, if you do 15% you're only removing 15% of the (whatever).... but that 15% can make all the difference in the world. I suspect even if the authors methods weren't flawed removing 25% of TOCs vs not removing any would do all the wonder in the world.
Click to expand...
plus ORP read alot higher with skimmer then without.


lapsan
 
Didn't read it through in details, but the variances are pretty high.

EuroReef CS80 needlewheel: 20 +/- 5 (6 data points); mean: 20; median: 18.5
ETSS Evolution 500 downdraft: 24 +/- 9 (5 data points); mean: 23.6; median: 17
Precision Marine ES100 venturi: 25 +/- 11 (4 data points); mean: 25; median: 24
Precision Marine AP624 airstone: 31 +/-5 (4 data points); mean: 30.5; median: 32.5

The range is pretty low, from 20% all the way up to 36% with a very small sample set. Too bad the protein they used (bovine protein) makes it cost prohibitive ($5/skimmer run), as I'd like to see an increased sample size to see how this number would normalize out.

If anything, this just shows me which skimmer to get if I was to chose among the 4.
 
sfsuphysics said:
Well you might say why do water changes at all too, if you do 15% you're only removing 15% of the (whatever).... but that 15% can make all the difference in the world. I suspect even if the authors methods weren't flawed removing 25% of TOCs vs not removing any would do all the wonder in the world.
Click to expand...

But it appears that skimmers don't remove 25% of each type of organic compound, but rather 25% of the types of organic compounds are removed entirely. Therefore skimming is having no effect on the majority of organic compounds many of which may be, i.e., alleopathic.

So if carbon can remove essentially all of them, so why not just use that?
 
Gomer said:
one thing which immediately comes up is the identity of what IS removed. Amounts only matter if all things are equal. If the skimmer only removes 25%, but it removes the bad 25% which cause detriment to the tank, then we have a totally different argument.
Click to expand...

Is there any evidence that that's the case? I'm not saying it's not... I'm just wondering. :)
 
orientalexpress said:
sfsuphysics said:
Well you might say why do water changes at all too, if you do 15% you're only removing 15% of the (whatever).... but that 15% can make all the difference in the world. I suspect even if the authors methods weren't flawed removing 25% of TOCs vs not removing any would do all the wonder in the world.
Click to expand...
plus ORP read alot higher with skimmer then without.


lapsan
Click to expand...

ORP really isn't the best measure of water quality ;)
 
Solid skimmate (weight %): total = 55.84

I'm wondering whatever happened to the 45.16% of the remaining dry weight and what was its composition.
 
Even I would not run a skimmerless tank until its at least a year or two old. : ) - but on my current tanks I run carbon and do water changes only now.
 
from the 2010/1 one

Only about 20 - 30% of the measurable TOC in reef tank water was removed by skimming, whereas almost all of the BSA was removed from saltwater by skimming.
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I'm not sure if the removal of BSA is good or bad, but seems like the removal of almost all of it would be a good thing. Granted it's a test parameter used to mimic proteins... but it seems that a PROTEIN skimmer, does in fact remove PROTEINS :D
 
It's NOT protein skimming, I despise that moniker. From one of my old college textbooks:

"many surface-active fractions of the DOC can be concentrated and removed in foam produced by foam fractionation. This process is also called airstripping and protein skimming; the latter is inaccurate in implying that only proteinaceous substances are removed" -Stephan Spotte
 
Ibn said:
Solid skimmate (weight %): total = 55.84

I'm wondering whatever happened to the 45.16% of the remaining dry weight and what was its composition.
Click to expand...


Particulate organics entrapt in foam I would guess.
 
well I'll admit I'm not a chemistry freak, in fact oil + soap is about the only reaction I really understand in cleaning :D

However your textbook quote
is inaccurate in implying that only proteinaceous substances are removed
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I wasn't implying ONLY proteins were being removed, but they are in fact removed with apparent great efficiency according to the AA article.
 
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