Humus, humic acid and natural chelating agents

Subject: Humus, humic acid and natural chelating agents

> What Craig is saying is that the activated carbon does not absor
> the trace elements, it absorbs the humic acids (and presumably t
> other chelating compounds such as EDTA). If the humic acids cont
> 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 o
> humus (source of humic acid) or soils in the substrate which con
> humus (such as laterite which we strongly suspect has ADDED humi
> acid!!) then there is an opportunity for the Fe to be resolubali
> An undergravel filter or plenum would interfere with this proces
> and so those people using UGFs are more dependent upon the use o
> chelated Fe nutrients added daily (or minimally bi-weekly). Som
> folks rarely need to added extra nutrients if they use a primari
> soil substrate (perhaps enriched with composted manure).

Why do you think a plenum would interfere with this process?  I 
agree that a traditional UGF moves enough water through the 
substrate to keep conditions aerobic. (that is its purpose) I 
can't see how a plenum would effect the anaerobic nature of the 

Karen Randall
Aquatic Gardeners Assoc.
Boston, MA