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Re: Sand

"David A. Youngker" <nestor10 at mindspring_com> wrote:

> And point number 3 leads to aesthetics - after all, you observe that plant
> growth and tank health aren't affected. But the presence of anaerobic
> activity still troubles you...

Hi, David,

Only in the sense that I don't have any experience that would hint me on
how it is going to evolve in the future. There are hints that it is getting 
worse, that is, larger and larger areas of the substrate are showing signs 
of anaerobic conditions (H2S bubbles and black stuff). If it stays under 
control, that migth be OK. But I would definitely feel more confortable
with _no_ H2S and black stuff !

> At this time, I'd say a comparison of techniques is in order. You're doing
> something very different than I am with the same materials and we're getting
> divergent results. In my view, sand *is* a viable, long- term substrate
> requiring very little intervention on my part - only the occassional
> addition of substrate fertilizer. But in order to determine where our
> divergence occurs, some more information is necessary.

OK, here is a description of the substrate: lower layer is 1 1/2" deep, 
silica (pool filter) sand mixed with crushed vermiculite (originally a 11 
qt bag) and 40 oz Substrate Gold. Mid layer is 1" silica sand. Top layer 
is 1/2" 2-5 mm river gravel. The entire thing sits on top of a UGF plate 
covered with a thin layer of foam to prevent the fine mix to seep thru 
the plate. The original idea was to provide low-flow reverse circulation. 
It didn't work in practice because at low-flow conditions channels form
and divert all the water thru a few spots. I keep it running anyways
to avoid a dead spot situation under the plate.

With time the substrate collapsed by about 1/2". Due to compaction, and
not seepage thru the plate (I can see under the tank). I can't tell if
the compaction was due to the presence of vermiculite or not. Both layers
seem to have gotten thiner, and the gravel layer partially got mixed with
the rest, but it's hard to tell. Could it be that the reverse water 
circulation contributed to compaction ? It sounds more likely that, if 
anything, it would counteract any compaction tendency.

Anyways, as the substrate got more and more compact, there was a slowing 
in the growth rate of most plants, the gradual disapepearance of pearling, 
and the appearance of the anaerobic zones, that now are pervasive. Plants 
still look healty and do grow, but at a much lower pace than before. When
sticking my fingers into the substrate I cannot tell it is in any measure 
more compacted, but it definitely feels much colder than the tank water.
For all that time (about 1.5 years) I tried to keep the same maintenance 
routine. I don't replant very often (maybe this is part of the problem ?), 
but I do use Jobes sticks and iron tablets on a regular basis (besides PMDD). 
I do a very ligth vacumming about once a month. 

What do you think ?

- Ivo Busko
  Baltimore, MD