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Re: Re: more red clay stuff
>1. If it doesn't settle well in a jar of water, won't it make a
>mess in the aquarium? George posted recently about reports of a
>potential bad batch of Dupla laterite clouding the water. And I
>understand that AP laterite does that, as well. Or does *good*
>stuff just kinda get stuck to itself and to grains of gravel, and
>therefore is not very mobile?
>
>2. Why won't the clay settle if it is any good? Is this from a
>CEC point of view? I did a shake test on generic all-natural
>kitty litter (Grand Union brand), and found that the stuff
>settled within minutes, and the water became clear. So would
>that imply that kitty litter is no good (my apologies in advance
>to Dan Q.)? Is it the particle size that's so important? I've
>done rudimentary shake tests on various topsoils, as well, and
>they typically settle much faster than my 100% clay samples did,
>even when they have a noticeable clay content. So I wonder what
>this means for using topsoil in aquariums. Obviously, a high-CEC
>substrate alone isn't enough, because, according to Jim Kelly,
>pure vermiculite doesn't work very well, but vermiculite mixed
>with topsoil that is high in fine clay particles works wonders.
>What's the magic -- small particles with *reasonable* CEC coupled
>with high iron content?
OK. Let me see if I can field this one. First the theory and then some
fact. I would think the best form for the iron would be that closest to a
liquid form. The smallest particles would be easiest to assimilate by the
root system. The finer the iron rich clay, the better the root system can
assimilate it. But here's the rub. Won't the smaller particles stay in
suspension longer and cloud the water. Yes; if it were not for a process
called flocculation.
Now for the fact. Clay particles in suspension exist in a charged state.
This charged state causes them to repel each other. Sufficiently small
particles do not settle because the force of gravity is not sufficient at
their size to overcome the other forces in the liquid that is keeping them
in suspension(their own charge, Brownian movement, etc.) However, the
potter overcomes this problem by adding materials to the suspension which
causes the particles to group together or "flocc" together. This increases
the mass of individual particles causing them to settle. The material used
by the potter to cause the particles to "flocc" is an acid or a base which
acts as an acid. Such common acids as vinegar will cause the particles to
flocc.
The flocculation process is very tricky to control. Not enough acid and
the particles do not flocc. To much acid and the process is reversed
because of the ionic characteristics of the contributing acid molecule. I
have not measured the pH of a properly flocculated slip solution but I
expect it is near neutral.
Now for some more theory. What to do about the cloudy water. I think the
correct answer is nothing. This is probably occurring in a tank with young
water. Leave it to age and the natural acid which accumulates in the water
as it ages should cause the clay to settle all by itself. If you can't
wait, increase your CO2 fertilization slightly to drive the water slightly
acid.
Regards,
Onis
k5vkq at ix_netcom.com