Re: laterite - any alternatives suitable

> From: Marque Crozman <marquec at gastech_com.au>
> in Sydney, various companies sell a product known as chelated iron 
> (FeEDTA) and another called iron sulphate; could these be used in a suitable
> mix with the lower section of the gravel to provide a fertile subrate that could
> mimic the more common laterite/gravel substrate.

No I definitely would NOT recommend using either FeEDTA or iron sulphate
in a substrate. FeEDTA is fairly soluble and won't provide a long term
source of Fe. Iron sulphate may be fine for terrestrial plants but in
aquariums, we should avoid the use of sulphate based substrate fertilizers.
In a highly anoxic environment where anaerobic bacteria are active,
sulphates can result in undesirable by products. Actually if you can
find it, ordinary iron oxide would be a much better choice in the substrate.
Many top soils are also rich in iron oxides and silicates. You could also
contact a pottery supply company and inquire about natural iron rich
clays. You should inquire particularly about any other additives used
to give special colors or properties to the ceramics which might not be 
good in a substrate.  Presently I have an experimental substrate using 
a pottery clay called Terra-Stone which comes from Alberta. I don't have 
the address handy but could get it if you really want it. I think you
will find a suitable clay closer to home without the high shipping cost.

In preparing the clay bottom layer I would suggest the following:

mix about half and half iron rich clay and fine sand 
for each 40 parts volume of clay/sand add 1 part of humus (earthworm

I also added a small amount of dolomite lime to attempt to bring the
pH of this mixture to a value close to 7. You don't want a pH above 7
I think but organic material like humus tends to be acidic. A pH
around 6.5 - 6.8 is probably optimal for the biological activities
we want.

Mix it up well into a thick mud. Allow yourself several days in
advance for the clay to soak in water to become soft or you're
faced with an hour or two of stirring. Spread this in a layer
about 1 inch in the bottom and cover it with sand or fine gravel
or other materials if you desire an organic substrate. Level it 
carefully with a small board or piece of slate. If you've
planned in advance and are not rushed, you can allow the mud to
dry and harden. 

This type of bottom layer is very low in organic material and
should not pose a problem with excess nitrate/phosphate leaching
into the water. If you intend to use a richer organic substrate,
then the organic materials should be concentrated in a second
layer above the clay layer. I've found that it might be wise to
plan two major water changes in the first two weeks of submergence.
Of course during this time there should be no fish since you'll
probably completely replace the water. If you don't plant during
the first week, you can also leave the tank dark to avoid algae
growth. Soft green algaes are probably going to develop and
several otocinclus will keep your tank spotless.

> Another question, would he be advised to just set up the tank without an
> additive to the gravel (using say PMDD instead) and would the substrate 
> heating still be as beneficial as with laterite?

I think the heating cables are most beneficial in a coarse granule
laterite substrate such as the Dupla laterite since the granules are
coarse enough to permit low circulation. The heating effect will also
improve the biological activity in a substrate containing some amount
of organic material such as various organic soils or the accumulation
of fish wastes. I don't use heating myself but have heard reports
of success with heating soil type substrates using the reptile
heaters. I can't tell you what the effects might be in a substrate
with a larger amount of organic material.