Re: nutrient diffusion into substrate.

> From: Charley Bay <charleyb at hpgrla_gr.hp.com>
> Anyway, does laterite intrinsically exhibit this well-aerated macro
> form?  I do not have the perception that it does; so even if laterite
> does not compact, I would naively bet that it does restrict flow
> (possibly) a magnitude greater than vermiculite.

If you used a layer of pure laterite, I have no doubt it would form a
dense compacted mass.  But in the aquarium, a small amount of laterite
is mixed with a large amount of gravel.  The gravel will not compact,
unlike the mashed-up vermiculite promoted by others.  The gravel
itself will provide the intrinsic, well-areated macro form that is so
desired while the small amount of laterite scattered around the gravel
voids will provide all the CEC necesary for excellent plant growth. 

After all, if vermiculite were so desireable, why would not Dupla
package it instead of laterite?  Surely, it would be cheaper to
package and would provide even higher profits than laterite. 

> I believe the point that Stephen.Pushak at hcsd_hac.com was trying to
> make was that he *could* trust vermiculite to passive circulation
> only, whereas he could *not* trust laterite to passive circulation
> only (or heat coils would be unneccessary).  Magnitude or not, these
> "clays" appear (to me) to be on opposing sides of some line.

Well, Stephen has apparently never seen laterite used in an aquarium
and I have never seen vermiculite used in an aquarium, so neither one
of us has any basis for trusting or not trusting either to do

Could someone explain exactly why water will "passively circulate" in
the verimculite?  This seems to violate some Law of Nature.  What
provides the energy for this circulation?  A reply on sci.aquarium
stated that "diffusion" will be ineffective at distances greater than
a few millimeters. 

What you seem to be saying (and I exaggerate here for effect) is that
there is something wonderful about vermiculite that nutrient-laden
water will find irresistable and the water will actively seek out this
substance, tunneling through layers of gravel just to have the
priviledge of being near it and sharing its nutrients with it. And, of
course, this very same water will find laterite so repulsive that it
will send its poor relatives, the Anaerobies, in its place.

Well, I guess this discussion has deteriorated to a religious war. Bummer.

George "Patron Saint of Laterite"