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George
To all and sundry:
George is not a spokesman for my views. I do not advocate timebombs nor
muck in aquariums. George seems to have missed my point entirely; I was
espousing iron rich materials such as laterite for their ability to
sequester phosphates. Go figure indeed. I contend that laterite is one
method for increasing the fertility of a substrate and that the Dupla
starter tablets added to the gravel are another. George is mistaken if
he thinks I am stating that his substrate or Dupla substrates are
infertile. Contrary to what George implies, I do not advocate excessive
quantities of organic material in a substrate. Note the use of the
operative adjective "excessive". Excessive means too much and is not
quantitative.
An alternative to using chelated iron additions to provide iron for
aquatic plants, is to use a substrate which can supply iron to the
rooted plants. Such a substrate requires a sufficiently low redox
potential to reduce ferric iron to the ferrous state. Paul Krombholz has
said a peat+soil mixture is able to perform this function much longer
than soil alone since the roots of aquatic plants over time, fill an
aquarium and increase the oxygen levels of the substrate. Paul used a
thin layer of soil+peat (less than 1") covered by a 1" layer of gravel
in trays and has been conducting such experiments for over 5 years (I
think it may be over 8 years). I've had peat in substrates for a much
shorter period of time.
Paul used a 50:50 ratio by volume of (fluffy) peat to soil. Peat itself
releases very few nutrients such as P or N upon submergence. Paul also
ensures that the soil he uses has a low organic content by the soil soup
method which involves straining out fibrous material.
Such materials as fresh leaves, compost, manures etc. are very labile
and will release LARGE amounts of nitrogen and phosphorus when they
decay. There are some occassions where controlled amounts of dried,
brown leaves, compost etc may be used for specific plants to encourage
lush growth but as a general rule, these materials are unsuitable for
the average aquarium.
Paul has also said that the peat-soil mixture may be unsuitable for
plants like A madagascariensis unless grown with companion plants which
raise the local redox potential in the substrate surrounding the lace
plant. If I recall correctly, he had one going like this for several
years.
In summary, there are several approaches which may be adapted to suit
particular requirements.
This whole laterite flame war is getting too personal IMHO. I'd love to
say something pithy in response to George but I won't. My opinion is
that he is taking perceived criticism of laterite far too personally.
Steve (Pushak)