Take a look at this article on what Skimmers pull out:
http://www.advancedaquarist.com/2010/2/aafeature/view?searchterm=skimmer
Most of the skmmate isn't actually coming from the livestock.
Conclusions
The chemical/elemental composition of skimmate generated by an H&S 200-1260 skimmer on a 175-gallon reef tank over the course of several days or a week had some surprises. Only a minor amount of the skimmate (solid + liquid) could be attributed to organic carbon (TOC); about 29%, and most of that material was not water soluble, i.e., was not dissolved organic carbon. The majority of the recovered skimmate solid, apart from the commons ions of seawater, was CaCO3, MgCO3, and SiO2 - inorganic compounds! The origin of these species is not known with certainity, but a good case can be made that the SiO2 stems from the shells of diatoms. The CaCO3 might be derived from other planktonic microbes bearing calcium carbonate shells, or might come from calcium reactor effluent. To the extent that the solid skimmate consists of microflora, then some proportion of the insoluble organic material removed by skimming would then simply be the organic components (the "guts") of these microflora. These microflora do concentrate P, N, and C nutrients from the water column, and so their removal via skimming does constitute a means of nutrient export.