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Redox potential and plant growth

My question about redox potential (so aptly answered by Bill and others,
thank you!) was from reading an article "A Planted Tank Aquarium for
Discus" by Jorg Ohliger, translated by Paul Ceroke, in the Spring 1997
issue of Discus Brief.  In the section describing a slow filter (a new
term to me) the author states "... Oxygen consumption by the bacteria
decrease the dissolved oxygen...and so that some already precipitated
trace elements can undergo chemical reduction and redissolution thereby
helping plant growth."  A translator's note follows: [in chemical
reduction, the oxidation state of the metal cation, for example iron,
Fe+3 (low water volubility) is reduced to Fe+2 (highly soluble).  The
higher the dissolved oxygen (higher redox voltage), the greater the
tendency for many metals to increase their oxidation state, but these
higher positively charged cations are less water soluble.]  The author
then goes on to say "...a slow filter prevents the redox potential from
rising too high where the plants cannot grow." 

How does this relate to dissolved O2 in planted tanks?  The article
appears to suggest a relationship between O2 concentrations and redox
voltage and redox potential?  Would the above mean that at high O2 ppm
approaching saturation, the more soluble form of Fe is less available to
plants, hindering their growth?  Is this a legitimate concern?  Bill
Ruff states other problems (such as plant and animal tissue damage) that
too high a redox potential can cause.  Does all this mean that O2
saturation is not as desirable a thing as I once thought, or are there
other factors, unrelated to dissolved O2 that contribute to undesirably
high (counterproductive, damaging), redox potentials? hmm.  Is it
possible to reach the redox potential limits of the proper range for
aquatic life in our tanks with too high an O2 content?  My tanks are set
up for discus, temps are high, 84 to 86, (high temp = lower O2 = lower
redox potential) and PH low, 6.1 to 6.6, (low PH = higher redox
potential).  Could tanks with low temps and low PH run into redox
potential problems?  What _is_ the proper redox potential range? And how
do we measure it?(without buying another meter) or do we really need to
care? :) 

Ed Hengel