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Trace Elements and fulvenes
Good morning everyone,
Last evening I was re-reading some old copies of "Today's Aquarium" (put out
during the 80's by Aquadocumenta in Germany and Edited by Kaspar Horst of
Dupla). I really used to enjoy that periodical - I wish that they could be
persuaded to put out an English edition once again.
Anyway, in issue 4/87, Dr. Gerd Kassebeer wrote an article on Trace Elements
in the Aquarium, and I'd like some opinions on what he said in it from you.
Anything in quotes here is from the article.
"All trace elements other than iron and manganese are easily dissolved under
aquarium conditions and are not transferred to the higher oxygen levels,
where they become insoluable."
- This may be a case of bad translation from German to English, but is he
stating that trace elements are not oxidized in an aquarium environment (and
thus made unavailable to plants)?
"Dissolved bivalent manganese is oxidized to the insoluable quadrivalent
variety not through dissolved oxygen direct but by special species of
bacteria which gradually collect in the filter.
...
Mineralization of waste products by bacteria consistently releases trace
elements. The higher the oxygen content of the aquarium water, the more
intensively are waste products decomposed and trace elements released.
As already mentioned in the case of Copper, plants, mud, and filter sludge
absorb trace elements and store them. Sometimes this process is reversible
so that the filter sludge works like a buffer."
- Could this process, if in fact the statement is true, be the reason why,
in the days of old when we used to maintain plant tanks without all of the
high tech gadgets and special fertilizers, aquarium plants would only REALLY
do well in a tank after a considerable amount of mulm had built up in the
substrate?
"Iron is practically always trivalent and insoluable under aquarium
conditions.... Bivalent iron is easily soluable at pH 7 but is oxidixed in a
matter of seconds by the dissolved oxygen present into trivalent, which then
flakes out as hydroxide and is filtered off."
- Seems like a case for the use of EDTA. But he goes on to mention other
possibilities...
"It is also possible for iron to be held in solution by complex-formers
(chelators).
...
Complex-formers are water soluable organic compounds which envelope the
heavy metal cations in such a way that they remain in solution.
Natural humins, the fulvenes, color the aquarium water yellow and produce
organic substances in the filter and sludge through bacterial decomposition.
They themselves are biologically degradible only with relative difficulty
and are natural complex-formers."
- Could tannins, released by peat or fallen leaves, act in the same way here
and act as natural chelators within an aquarium environment (or for that
matter, a natural environment)?
Kassebeer goes on to discuss the fact that "bound" micronutrients are not
absorbable by the plants and that there is some "suspected" method whereby
the plant makes it's own "complex-formers" which act as the transfer
mechanism to get the micronutirents into the plant tissue. He further
discusses the addition of EDTA and states that under certain conditions
(i.e. excess) it can precipitate iron hydroxide, which increases with time.
Precipitation, he claims, has a side effect of "carry-down precipitation".
"...The colloid produced absorbs not only phosphate but all the heavy metals
in the water... In this case the trace elements can easily be removed from
an aquarium."
- Could an excess of natural humins, such as fulvenes and tannins, do this
as well? Could this be one of the resons why "blackwater" habitats in nature
sometimes exhibit such low mineral content and why plants don't grow very
well in a really "black" blackwater environment? Are all of the
micronutrients being sucked out of the water by this action?
Something to think about, anyway...
James Purchase
Toronto, Ontario