Re: nutrient diffusion into substrate

> 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. 

Laterite is more exotic.  ;^>

Seriously, though, I realize that vermiculite has almost no nutrients
to offer initially (the stuff is sterile).  Laterite has high Fe+,
and a host of other elements in macro- and micro- form.  This is
the greatest appeal that laterite has for me:  It's hard to go wrong
when you know you have such good concentrations in the substrate.

All the thoughts I've seen here on vermiculite are really centered
around the (speculated) possibility that vermiculite can be 
sufficiently charged with nutrients (since its CEC is so high),
and that its porous nature would provide greater opportunity for
aerating the substrate.  I believe these are valid points worth

> 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
> anything!   

I guess we need some more data points.  :^)

> 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. 

I think there are at least two issues. (1) Will the substrate go
anaerobic without circulation intervention (passive diffusion is 
sufficient, no heat coils), and (2) will nutrients enter the 
substrate passively (through diffusion) in sufficient quantities 
to replenish those nutrients adsorbed?

My opinion (my guess, really) is that (1) is "yes" for laterite, "no"
for vermiculite, and (2) is "not relevant?" for laterite, "I don't
know" for vermiculite.

While diffusion may not be adequate for nutrients (I don't know), 
it surely must be for O2 (too many tanks on this list have 
substrates that have *not* gone anaerobic, even though no circulation
method was employed).

> 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"

No, I don't want it to become a religeous war.  I really want to
get some input on whether the inherently porous nature of vermiculite
will allow for old substrates to remain sufficiently oxygenated,
and that in time, nutrient supplements can charge the high CEC 
potential of vermiculite to a point at least equalling laterite.

In short, I *honestly* want to know that long-term, can vermiculite at 
least equal the effectiveness of laterite because of its higher
CEC and more porous nature? 

charleyb at gr_hp.com	or	charley at agrostis_nrel.colostate.edu