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Re: Sand substrate

On Mon, 5 Feb 2001, Paul Kelley wrote:

> Also I've been thinking about adding organics to a two layer substrate. The
> bottom layer will be, one part Schultz's aquatic soil (a laterite material,
> baked clay) to roughly two parts neutral sand. This layer about 1.5 inches
> thick. Covered by regular gravel, another 1.5 inches.

> My thought is this: mix some potting soil, say three parts sand to one part
> potting soil and one part peat, and laying it on strips of cheese cloth in a
> thin layer, perhaps 1/8 inches thick.
> I would then roll the covered cheese cloth up and make tubes from 1/2 to one
> inch round. Place those in the bottom layer at regular intervals. Idea here
> is to make the nutrients available to the roots but lower the risk of
> contaminating the water column.

Paul, I think you may be a little too worried about letting the potting
soil and/or peat moss move around.  Neither peat or potting soil -- once
water logged -- makes much of a mess; the dust and clay from other
substrate materials is probably much worse.  I boil peat and potting soil
to get it water logged faster (it smells bad), but just mixing it with
gravel seems to be enough to hold it down until it gets water logged on
its own.

Also you should know that many (all?) peat or potting soil mixes
will color your water.  Normally this is just a light amber color that
goes away after a few weeks.  If you do something to circulate water in
the substrate then the color can get much darker.

If you want to mix sand into the substrate then probably you should use
only a small amount of sand.  In a substrate composed of clean gravel,
about 35% to 40% of the substrate volume is actually pore space.  I think
that space is wasted.  On the other hand, substrates that are composed of
pure fine sand or organics has a tendency to compact and then block
circulation in the substrate.  I think you can find a nice middle ground
by mixing aquarium gravel with about 15% to 20% by volume fine sand,
potting soil or peat.  The sand and soil sifts into the pores of the
gravel and fill up some of the empty space (but not enough to completely
block it) and the gravel keeps the mixture from moving around.  Cap that
mix with a little clean gravel or gravel mixed with coarse sand and you
have an attractive topping for the mix.

I have three very successful tanks set up with that substrate.

Simple is good, too.  I haven't tried commercial aquatic plant substrates
(e.g. Profile or Flourite), but a lot of people report good success with
substrates made up wholly of those products, or with those products capped
with gravel.

Don't worry too much about anaerobic spots in your substrate.  Plants are
adapted to handle anaerobic conditions, and in my tanks I find that many
plants grow better where they can extend their roots into anaerobic zones.
Some plants even seek out anaerobic zones.

As to the question of fine substrates in general... Some plants seem to
grow better with fine substrates than with coarse substrates.  I'm
thinking particularly of lilleaopsis and marsilea - both small, shallow
rooted plants.  They seem to be an argument in favor of using fine sand
in a substrate, but in their case the sand would have to be at the top of
the substrate, not at the bottom or middle.

Roger Miller