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[APD] Re: Flourite, clay and soil

> From: "Robert H" <robertph3 at comcast_net>
> Flourite is baked clay. Not soil.

You will find several definitions of clay in a dictionary, including
items made from fired clay.

> What exactly is Flourite made of? What type of clay?
> All I can say is that it is a naturally mined clay (i.e. it is not
> "manufactured").
> What is the significance of "fracted"?
> Basically a fancy way of saying the clay has been shattered
> or broken into
> many small pieces of suitable size for a planted tank.

If the material is rigid rather than powdery and is dug out of the
ground in that form, it's probably better to classify it as shale. The
actual mineral composition can still vary greatly so I would suspect
that SeaChem has gone to the trouble of finding dirt that is low in
calcareous materials (calcium and magnesium), low in toxic heavy metals
and high in iron. To get clay particles to bond together without the
application of heat, would probably require lime as a binding agent.
Pottery clay typically contains a certain amount of calcium and
magnesium however this varies greatly and determines the type of pottery
that is made. Iron rich clay makes terracotta with the rich red color.

If the rock/dirt is volcanic in origin, and is bonded together by heat,
then I don't think its proper to label it as clay.

Dirt is simply the broadest category of all types of stuff that you find
comprising the ground and so, to be picky, includes all other categories
of soil, clay, sand, gravel, laterite, fluorite etc.

Soil, on the other hand, generally can be considered to be something
suitable for growing terrestrial plants upon and would typically
contain, in addition to mineral particles, a proportion of fully
decomposed organic material (humus) and partly decomposed organic
material (fibres, dried fragments of leaves, assorted organic remnants
AKA compost) The longer the organic material has been composting, the
closer it is to being humus. Black soil contains lots of humus. When a
fruit or bit of kitchen waste is tossed into the compost heap, its quite
high in nitrogen and other organic nutrients. As bacteria and soil
organisms (insects, worms, nematodes, beetles) break down the compost,
these nutrients are unlocked and become soluble (mineralized) and
typically leached away by the rains. Of course some of the nitrogen in
the form of nitrate or ammonia remains captured by weak chemical bonds
within the humus. Earthworm castings are relatively fertile for instance
even though they are pretty well along the road to becoming humus. The
"fresher" the organic material, the more attractive it is to a more
diverse population of composting organisms and the greater is the demand
for oxygen. The technical term for "fresher" is labile. Labile =

When Tom talks about providing a source of carbon in the substrate, he
is referring to organic material of some type which bacteria can act
upon and which will release CO2 as O2 is being consumed to "digest" the
organic material. Organic material comes from living things and is
always carbon based. Organic chemistry is the chemistry relating to
compounds of carbon.

When you put a labile material such as soil containing compost, or
topsoil in the aquarium substrate, you are creating a source of CO2 and
a sink for O2. When you have aquatic plants growing actively in the
tank, you have a source of O2 and a sink for CO2; things balance out
quite nicely so that oxygen levels remain high in the water but low in
the substrate. Of course, with any amount of rotting material, its going
to produce a small amount of noxious organic by-products.

The beauty of peat is that it has been leached of soluble minerals for a
very long time and so what is left is the toughest and most resistant
parts of the plant fibres, the lignin and cellulose. In a low oxygen,
acidic environment such as a peat bog, the stuff lasts virtually
forever. Add some oxygen and some nitrogen, such as in an aquarium, and
bacteria will begin breaking it down. As an organic source of carbon in
the aquarium, peat is ideal because it does not contribute any
"unwanted" by-products. As a source of nitrogen, well it doesn't have
any, unless you went to the trouble of pre-soaking it in nitrate

> Does it provide a source of Fe? In what form?
> Yes. Ferric mainly.
> Does it need a chelator?
> No, the plants roots are able to extract all the iron they
> need directly
> from the Flourite (just as they would extract from the soil out in the
> "real" world).

You can read about how plants use enzymes and organic molecules to
convey iron and other nutrient ions by perusing some of the articles
hosted on my website or by following the links there. I apologize for
the fact that my links are probably out of date and so the targets may
not be in the same locations. Plants grow just as well whether you know
about the theory or not.


> Soil on the other hand can be full of trace minerals, and
> organics that
> provide nitrogen. Top soils and potting soils are very high
> in organics
> usually in the form of manure, compost, worm castings and
> such.   What is
> often called "Sub soil" the layer of soil under the leaf
> litter has less
> organics.

I think I need to make a small correction here. Top soil is the top
layer of soil and usually is relatively high in organic material
primarily humus. Once you dig down a few inches or a few feet, you will
come to another layer of soil, AKA subsoil. As you dig down further, you
will find other layers of varying colors, also known as soil horizons.
You may find light colored layers which indicate that calcium has
leached into this layer. Generally you can say that subsoil has no
organic material in it and will be extremely low in soluble minerals
such as nitrates or available phosphates.

Do you want (low lability) subsoil, topsoil, earthworm castings, compost
or manure (high lability)? It depends upon how much, if any, nitrogen
and labile material you want in the substrate. It is very easy to
control the amount of nutrients in the water of the aquarium by the
simple expedient of regular water changes and adding small doses of dry
minerals to the water. Whatever is coming from the substrate is not
controllable unless you can have a continuous water change system. If
you have very fast growing plants such as lace plants, it may be easy to
use a labile substrate. If you are growing Crypts or Anubias primarily,
then you probably want to avoid rich, labile substrates or you will be
liable to grow more algae than plants. ;-)

Crypts and Anubias still benefit from nutrients in the substrate; its
probably best to use the clay fertilizer ball approach than earth worm
castings, or to put the soil into pots.

> Using large amounts of top soil can be dangerous in an
> aquarium because the
> decaying organics can cause problems...

Usually you will find people suggesting an inch or two of soil. If you
had say 6 inches of earth worm castings or soil with compost in it, you
could certainly expect to get some noxious by-products. Many of the
aquarium denizens could probably tolerate it especially the Cory catfish
and other critters adapted to low oxygen environments. At the other
extreme, salmonids and other cold water, high-oxygen fish would not fair
well in such conditions. Plants for the most part would not care too
much if the oxygen levels were low or high. Many of them can grow their
roots down into some very stinky muck and flourish in that environment.

Most of our aquarium plants can manage to look fairly decent growing
under relatively unfertile conditions and this is the easiest way to
avoid problems with algae, particularly BGA which thrive when there are
more nutrients or organic pollutants than the plants & biota can break
down & consume efficiently. Peat provides a source of beneficial organic
compounds: humic acids, tannins, organic acids, which are useful to
plants as chelating agents for iron and manganese. Humic acids and other
organic molecules also react with "toxic" minerals such as copper to
reduce their chemical reactivity, thereby reducing their toxicity. Most
people don't have to worry about heavy metals in their water but its
nice to know that if you are digging your own dirt, that adding some
peat to it, may help prevent problems if that dirt were slightly high in
lead, copper, manganese etc. Think of peat as a sponge that grabs and
holds all kinds of dissolved minerals especially calcium and magnesium,
the most "attractive" of dissolved cations.

Now I haven't given anyone the answer to the "perfect" substrate. I can
suggest that you use peat and some other non-organic type of dirt to be
"safe". Clay, subsoil, sand, gravel, Fluorite, laterite can all be
considered non-organic. The differences will arise primarily in texture
and composition. In terms of composition, you will generally want a type
of dirt that is relatively low in calcium and magnesium but high in
iron. A little manganese, copper or zinc can be good but too much is
deadly. In general, soil from an arid region that is alkaline is also
likely to contain undesirable minerals such as lead, mercury, arsenic
and the like. Soil that is well leached, and low in calcium will also
not contain toxic metals. That's one reason laterite is attractive; it
has virtually everything leached out of it.

When do you want to play "unsafe" and use a more fertile substrate? In
most cases, you can give plants a big boost of nitrogen and phosphorus
by using clay fertilizer balls and you wouldn't need to use a rich soil.
There are some plants that are prodigious consumers of nutrients. When I
learned that the guys having the big success with Lace plants were using
manure in their substrates, it was a revelation! Here is a seasonal
plant that wants to grow prodigiously and store huge reserves in its
rhizome for the off-season! OTOH, a very respected botanist friend of
mine feels that the Lace plant does not adapt well to the anaerobic
substrate. I can't say for sure but I know that the two specimens that I
have only flourish if I give them regular feedings of nitrate in the
water, in addition to the soil and clay fertilizer balls for the roots.
I don't have enough spare Lace plants yet to experiment with truly
labile substrates however I think that the plant could adapt if allowed
to grow into its rich substrate. The real trick of course is in keeping
the algae in control or in preventing its introduction entirely. This is
easier said than done. :-)

Just another perspective.

Steve P in still hot, sunny Vancouver

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