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Iron and substrates

Bob Dixon wrote:

>So what percentage of iron content is necessary in a substrate additive like
>laterite or other clay if one wants to maintain a tank without teardown over
>an extended period of time, say foive or six years?  I realise this is
>conditional on the size of the tank, the amount of substrate additive, the
>types and quantities of plants, etc, etc, ad infinitum, but can someone
>generalize on an average tank of a nominal size, say 55 gallons, or maybe 100
>gallons with a given substrate additive level as recommended by say, Dupla
>(wouldn't that be like 10 g. per gallon, mixed into a one inch layer at the
>bottom of the substrate)?

I've said this before, and I'll say it again.  I have _never_ had a
laterite based substrate of _any_ size "give out".  I have had tanks
running as long as 8 years.  Those with shorter life spans have been taken
down for moving or changes of tank size, etc., never because I felt they
had "given out".  I use laterite in the amounts recommended by the
manufacturer.  You don't need huge amounts to do the job.

>And has anyone actually tested the iron content in their substrate additive
>before setup and again after a couple years, in order to demonstrate that
>is indeed coming out of the clay?  Or are we all assuming that the iron thing
>Dupla has sold us on is actually happening?

Dupla recommends regular supplementation with iron.  I know it is possible
(through neglect<g>) for plants in laterite based tanks to become iron
deficient if they do not receive periodic supplementation.  Likewise, it
has been my experience that JUST using liquid supplementation in a tank w/o
laterite doesn't do the job for most root-feeding plants.  So whether the
mechanism is what Dupla thinks it is, or whether something different is
going on, I won't even guess at.  The fact of the matter is, the system works.

>Some folks, I think Karen is among them are not using substrate coils.  Do
>these tanks deteriorate after a given percentage of substrate iron is
>depleted?  Or do the keepers of these tanks simply recognize iron deficiency
>symptoms and suplement into the water column successfully?

As I said, I've never seen any substrate deteriorate to the point of being
unusable.  I think _most_ substrates require the addition of supplemental
trace elements from time to time, although it may take longer for some to
need this than others.  Even Steve P., who is a strong proponent of soil
substrates as a means of providing most nutrients for his plants admits to
at least occasional supplementation.<g>

As far as cables are concerned, I have had limited experience with them,
and none with commercially made systems.  I do know that in a heavily
planted tank with good growth, the plants themselves draw water down into
the substrate.  (actually, they draw water OUT of the substrate and into
their tissues, which is then replaced from the water column above)  This
process certainly seems to be adequate for excellent growth.  I'm not in a
position to say it couldn't be BETTER with cables, but it can be very, very
good without.

The only substrates that I have heard of that have actually "gone bad" have
been poorly designed to start with, (too much clay or too much organic
material) and/or in tanks without adequate root penetration, i.e. tanks
that are not heavily planted and growing well.

Karen Randall
Aquatic Gardeners Association