What is DOC?

All of us who keep reef aquariums are familiar with nitrates and phosphates but Dissolved Organic Carbon compounds and their role in aquaria are still pretty much unknown.  To start with I thought I'd list some basic terms:

Dissolved Organic Carbon, DOC.  There are literally thousands and thousands of different compounds that fall under this label.  None of which can be tested for at the aquarist level.

Particulate Organic Carbon, POC.  POC is organic compounds that typically are larger than .45 microns.

Total Organic Carbon, TOC.  TOC is the sum of POC and DOC.  Generally DOC makes up ~90% and POC is ~10% of TOC.

Dissolved Organic Matter, DOM.  As near as I can tell from the research I've read DOM and DOC are synonymous.

DOC is further subdivided into:

Labile DOC, easily metabolized by microbes and marine organisms.

Semi refractory DOC, can be metabolized but it is ineffeciently done so by microbes

Refractory DOC, being very difficult or resistant to being used or metabolized by microbes and marine organisms.

The ratios vary with depth between these three general forms of dissolved organic carbon but at the surface the refractory makes up roughly 70% of the DOC that is present. 

 In our aquaria both algae and corals are producing DOC compounds.  Interestingly, the DOC released by corals and coraline algae promotes autotrophic (oxygen enriching) microbial populations while the DOC released by algae promotes heterotrophic (oxygen depleting) microbial populations.  This is one of the reasons we need to think of our corals as autotrophs, a term normally only used for plants and photosynthetic algae.

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