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Condition of Plants in torn down vermiculite tank

To the Inquiring minds--

I tore down one of my two 8-month old vermiculite substrate tanks this
weekend, because some of the plants were not doing as well as I like. This
tank was intended to be low tech/low maintenance. Setups with added CO2,
more lighting could have produced better results. My other vermic tank with
peat instead of soil is still going strong and is providing better results.
However, results from the soil/vermiculite experience are inconclusive. 

Tank size: 40g, 36" x 18"w x 16"h
Tank location: two of these tanks are side by side, on metal stand over a
125gal tank.  Heat from 280w of fluorescent lighting over 125 provides heat
to tanks above.
Lighting(centered over the two tanks): shop light w. 2 40w bulbs(triton &
coolwhite), + 1 6-ft strip light w. two 30w. coolwhite bulbs. i.e. each tank
gets 70w lighting.
Substrate
   composition:(bottom half= 1/3 top soil, 1/3 verm, 1/3 coarse sand); top
half=coarse sand.
   depth: 2 1/2 inches
   supplements: occasional (bimonthly) DAI algae tabs or Jobes plant stick 
    (used to provide nitrogen and phosphates, before I learned that DAI has
N and P)
   Devices: No direct heating w. cables, UG plates, etc. 
   Condition:  some anaerobicity, indicated by slight sulfur smell; no black
coloration.
   Other comment: soil and vermiculite come to substrate surface when plants
are pulled out; not visually pleasing.
CO2: None added
Water Changes: 20% biweekly. My tap water is soft, 7.4 pH with 50ppm
carbonates (added lime during treatment), some nitrates, phosphates,
probably a good mix of several needed trace elements.
Water chemistry: I forgot to check final pH. :-(   Last time I checked, a
few months ago, pH was ~6.5-7.0, I think. No other measurements.
Algae: none noticeable
Plants: 
   Hygrophila polysperma; normal and sunset variety (lots), Echinodorus
quadricostatus, Vallisneria sp. (one of the 'giant' varieties,5 plants). I
can't remember the name; may be V. neotropicalis because it originally had
reddish color. The regular hygro grew like weeds and were harvested
bimonthly. The sunset variety grew more slowly, leaves were smaller and
crinkled in appearance; dark reddish color once plant reached half the water
column height. Noticeably different than longer and lighter colored sunset
leaf in other tanks. The chain swords were not doing well; produced small
rosettes, but propagation rate was slow and leaf length was ~ 1". (The
observed range in my tanks is 1 to 4 inches)    Roots of all plants were
white and in healthy condition. The Val's roots reached the bottom glass;
the leaves are all 4 feet long with 1/2 inch width.
Fish: Ameca spendens (20-30, 1/2"-1 1/2")), panda corys (1/2", 10); fed daily.
Conclusions (speculative): The plants may have been carbon limited (i.e.
needed added CO2 or decomposing organic matter).  The val did well, but its
leaves could be getting add'l CO2 from their length and position on water
surface. Lack of visible algae suggests possibility of other nutrient
deficiency.  Val may have been too competitive, either in terms of nutrient
removal or release of allelochemicals; they were also providing some
shading. Val would probably do even better in this tank if provided stronger
light; it did not maintain red color.  Soil could have been providing too
much of some trace element(s), creating 'toxic' condition for sunset hygo
and E. quadricostatus. Color spectrum of fluorescent lighting may have been
lacking.  Too many uncertainties, but I don't believe that vermiculite
contributed to the problem. At least, the substrate remained soft and permeable.

         Neil Frank, editor of The Aquatic Gardener
Visit the AGA home page at <http://blake.oit.unc.edu/~fish/aga/>