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Re: Vermiculite, Laterite & Terralit

Ryan Murray <rmm at acpub_duke.edu> wrote:
>  I have been trying to
> understand the function of laterite et al. as I am about to tear down
> and rebuild my 75g planted discus tank.  I do not want to attempt any
> oragnic material in the substrate yet but am interested in using some
> high CEC material such as laterite in the bottom 1/3 of the substrate.
> I am particularly interested in the difference in vermiculite and
> laterite in terms of this functionality.  While vermiculite does not
> contain
> iron (I gather but may be wrong) wouldn't it adsorb iron from the water
> column if PMDD style suplementation was used?  If so what is the
> advantage to using laterite over much less esoteric vermiculte?  Also,
> is there any consensus on the difference between tropical laterite and
> the US mined product (eg the A.R.T. clay stuff)? 

Vermiculite in my dictionary is defined as a hydrous silicate; as such
it does not contain iron except as trace impurities. Vermiculite has a 
flat layer crystal structure which causes it's extremely high surface 
area and volume. This low density is what distorts the CEC measurements 
which are measured in cations absorbed per kilogram of mass (not
If you are interested in improving the CEC of a substrate without using
organic material, I suggest the use of a mineral soil (e.g. iron rich
clay, screened soil, subsoil) without the disadvantages of vermiculite.

Vermiculite doesn't adsorb iron from the water.

Clays used for pottery contain large amounts of silicates which are
absent in laterite.

Laterite is mainly iron oxide and hydroxides but may also contain 
aluminum oxides and hydroxides. The CEC of laterite is about a hundred 
times less than humus or clays but many orders of magnitude better than 
clean gravel or sand. The important characteristic of laterite and 
mineral soils is probably iron which plays an important role in the 
sequestration of phosphates. Other mineral soils also contain a variety 
of other trace elements aside from iron. Refer to my TAG article for a 
complete and technical discussion of these materials.

> After I posted about the vermiculite/laterite comparison, I remembered
> an Aqualine Bushke product called Terralit.  Would anyone familiar with
> this product comment on using it instead of laterite or other substrate
> additives?  I saw mention of it in the archives but couldn't glean much
> about its nature/usefulness.

We don't know much about the ingredients in Terralit. Olga uses it with
very good results and I believe the box mentions trace elements which
would include iron and other trace nutrients. It might contain other
occluded macro nutrients. If someone has a small amount, they could add
it to a jar of water and test for nitrates and phosphates in a few

Steve P in Vancouver BC
teban at powersonic_bc.ca   <**** NEW EMAIL ADDRESS