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Red clay for the aquarium
One of the important properties of laterite and other soils used as
additives in aquatic substrates is the iron content. I suspect that
this is the primary reason that we can observe improved growth rates
and plant health in these enriched substrates compared with plain sand
or sand only enriched by fish wastes.
Another important factor in improved plant growth rates, and health is
the presence of additional nutrients (in moderation) in the substrate.
Excessive amounts of organic material or nutrients will result in high
concentrations of nitrates and phosphates in the aquarium water which
will encourage many kinds of algaes especially cyanobacteria
(blue-green "algae") and various filamentous algaes. Many aquarists
prefer to use peat as an additive for its resistance to decomposition
and relatively low levels of nutrients.
One of the negative attributes of clay is that if you are not careful,
you can create very cloudy (turbid) water. You should be familiar with
the precautions for using clay before you experiment with it.
The Optimum Aquarium (TOA) book is an excellent reference book
describing the use of laterite and provides an easy to follow, highly
repeatable methodology for growing aquarium plants. It is of course
somewhat oriented towards the Dupla product lines and there are other
easy and cheaper methodologies for growing plants. There are many
right ways of growing aquatic plants and the right method for you is
often a matter of taste and past experience.
Alternative sources for iron in the substrate include natural red
clays, most soils (except sand) and micronized iron which you can find
in gardening centers. Other trace nutrients (not found in laterite)
are found abundantly in many types of mineral soils including top
soil. Of course it is also fairly easy to provide those nutrients from
commercial products (eg. Dupla Drops, Tropica Mastergrow, Flourish...)
or from the PMDD recipe (discussed in the APD archives endlessly)
I prefer to provide most of my plant nutrients from the substrate
since it reduces my reliance upon regular dosing and frequent nutrient
concentration testing. You still need to provide Ca, Mg and K in the
water. It is often advantageous to supplement chelated Fe to some
degree in the water particularly with new or relatively shallow
substrates. Crypts may be adept at getting Fe from the substrate but I
don't think all plants do as well although almost all rooted plants
benefit greatly from iron, fine materials (silt, clay) and somewhat
higher nutrient levels in the substrate.
A forthcoming article in TAG on the subject of substrates by yours
truly should be coming out real soon now. If Neil Frank is currently
following the APD I hope he can give us an update since many of us in
the AGA are pining for our next issue of TAG! ;-)
Steve Pushak in Vancouver where the summer weather is just glorious