substrate experiences

Those of you who are interested in substrate performance may find something useful in my experiences (don't want to call them "experiments", with no control group or proper measurements):

In  May 1996 I set up a tank with a layer substrate of 1" fine red clay (from the Lake Norman area, NC) topped by 1" composted cow manure (N:P:K = 0.5:0.5:0.5)  and 1" medium fine aquarium gravel. Plants consisted of stem plants (Alteranthera, Hygrophilia, Bacopa, Rotala, and later Ludwigia), crypts (C. wenditii in 2 forms, C. griffitthii(?), Liliaopsis b., Valisneria, and the odd other. Light was in ample supply (120 W mixed flourescent). CO2 added via yeast method.

The tank did not go through any algae cycles, never did I have red algae, or green algae (untill I added infected plants :(  ). Initially, plant growth was phantastic. During the first few months, many gas bubbles came out of the substrate. I suspect that this was Nitrogen gas. I noticed that when the bubbles stopped, the plant growth slowed down too, and I needed to add PMDDs (with nitrates) regularily.

Last week I tore the tank down: it was increasingly difficult to move plants, their root systems were just too extensive. And the compost had finally started to move higher and higher making a mess of things.  As more compost was exposed to the water colum, green thread algae was exploding. I believe the
organics in the compost were releasing lots of phosphates as they were braking down. 
Now to the roots. I was interesting to see that the crypts (plants with 5 or 6 leaves) had roots/runners that were 10" long. Also, their roots extended mainly into the clay - 20% in the compost, 80% in the clay. On the other hand, most
stem plants and the vals, had relatively larger proportion of their root system in the compost than in the clay. The exception was Alteranthera reinecki and Bacopa carolinia. Their roots grew almost straight through the compost into the clay. The roots of Anubias nana var. lanceolata were much longer than others I've seen.
BTW, all the roots were either white (in the compost) or rust colour (in the clay).

Once all the water was out, there was no bad smell (i.e. H2S) coming from the substrate. I did notice a faint odour characteristic of submers/anoxic soils. So it seems it was quite healthy - _sufficiently_ oxigenated by the roots.

I set up the tank again with a much "leaner" substrate (gravel with a little clay, no compost), in containers. And a bleach bath (1:20 diluted 5% bleach) for everyone.... 

I do have a quick question though: Rotala macandra had deep red stems and leaves prior to the bleach (1.5 min). The following day, all the leaves were green. Is this normal?

in Waterloo, Ontario, Snow.