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Originally Posted by tmz 
I disagree with the last sentence. Depending on the ration of N to P in the bacteria removed, it is very relevant to the discussion of the thread.
Skimmers remove organics including bacteria. Individual orgniac compounds and organisms have variable N
ratios. En masse ,why would the content of skimmate have a different ratio of N and P than the tank? Seems it wouldn't; I don't think GAC would efffect the ratio either, overall. Not exporting organics likely wouldn't effect the ratio either;just the overall volume.
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If the individual organisms and organics have different ratios then the tank and are concentrated in the skimmate then it is it not conceivable that the skimmate could have a different ratio to the tank?
Scott, I'm late in answering ; been distracted with family health issues.
Anything is possible but there isn't any plausible reason I can imagine to think the C:N
ratio of the tank will be altered by skimming given the amphipathic nature of almost all organic molecules in a reef tank. Amphipathic moleucles are attrracted to the air water interface.
Organisms have protein which is attracted to the air water interface ,that is why a skimmer is called a protein skimmer,btw. .
Overall ratios in skimmate are very likely to be similar in C,N,P composition as the source tank water ,IMO.
A little organic chemistry regarding solubility shows why I think so.
Molecules in water range from hydrophyllic to hydrophobic:
Those that love water,(hydrophylic) and are bound to it (solubles like salt,sugar, ethyl alchohol, glycol ammonia ammino acids ,many inorganic compounds ). These are not attracted to the air water interface at the surface of the water in a tank or the the air water interface in a bubble of air in a skimmer's water column.
Hydrophobic molecules,those that are repelled by water( fats, oils, gasoline ,etc) are squeezed out of solution by the attraction water molecules have for one another and go to the air water interface forming surface films.
Like most distinctions the differences between hyrophobic molecules an hydrophylic molecules fall on a continuum .
In the middle are amphipatic molecules which have both hyrdorphylic and hydrophobic components ;proteins and most organic molecules in a reef tank fall into the amphipathic category.
The amphipatic molecules are attracted the air water interface.
" ...In actual practice, most organic molecules found in a marine tank will be amphipathic, with the bulk of the remainder being hydrophilic. There will be relatively few purely hydrophobic molecules (e.g., fat) in the tank. Most very hydrophilic molecules will not be removed by a skimmer, so understanding how amphipathic molecules react in a skimmer is the key to understanding how a skimmer works. One reason that skimmers are often referred to as protein skimmers is that most proteins are amphipathic. They often have an interior made from hydrophobic amino acids, and an exterior made of hydrophilic ones. When dissolved in water, only the hydrophilic exterior portions contact the water molecules. When placed in contact with an air interface (or something that is hydrophobic) the proteins will alter their shape, and present the hydrophobic portion to the interface. In this fashion they are readily attracted to an air/water interface..."
The above is per an article by Randy H. Farely
http://web.archive.org/web/20010309054900/http://home.mweb.co.za/jv/jv79/reef/skimmers2.html
So why would a skimmer select amphipathic molecules with C:N
ratios diiffernt on average as has been asserted than those in the tank .? I can't think of reason.
