Re: Humus, humic acid and natural chelating agents

> From: Craig Bingman <cbingman at netcom_com>
> > > Humic acids are removed by activated carbon.  There are clear 
> > > implications for fate of trace elements in aquaria, perhaps Espe
> > > freshwater aquaria, in that statement.
> > That's why few aquatic gardeners use carbon in their systems ;-)
> Ah, but I don't believe that I've ever heard anyone say that the removal 
> of trace elements is mediated by their removal as humic acid chelates.  
> And I also know of some experimental determinations indicating that trace 
> elements are not removed by activated carbon (in otherwise pure water) 
> except at extreme pH values.

What Craig is saying is that the activated carbon does not absorb
the trace elements, it absorbs the humic acids (and presumably the
other chelating compounds such as EDTA). If the humic acids contains
bonded Fe, it is removed from the system. Any remaining Fe++ in
solution would not have chelation and would rapidly be oxidized
to an insoluble state and precipitated. If there is humic acid or
humus (source of humic acid) or soils in the substrate which contain
humus (such as laterite which we strongly suspect has ADDED humic
acid!!) then there is an opportunity for the Fe to be resolubalized.

An undergravel filter or plenum would interfere with this process
and so those people using UGFs are more dependent upon the use of
chelated Fe nutrients added daily (or minimally bi-weekly). Some
folks rarely need to added extra nutrients if they use a primarily
soil substrate (perhaps enriched with composted manure).

Steve in Vancouver.