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Rataj and Horeman book
Jerome, from Buenos Aires mentioned the Rataj and Horeman book and
asked about undergravel filters.
This book is quite dated and the author held opinions about substrates
which should be taken with a grain of salt. He suggests that garden
soil, peat or clay should never be used in aquarium substrates and he
misleads many many aquatic gardeners by suggesting that oxygenating
the substrate by undergravel filters is important. I consider this
poor advise since there are great advantages to using substrate
additives such as small amounts of: laterite, clay, soil or peat. I
also believe that plants are the best method for controlling the
oxygen content (or more properly redox potential) of the substrate.
One must understand the precautions for using such substrates.
Substrates should not contain too much organic material (consider 5%
optimal) and you do need to have a healthy initial planting with all
of the other conditions necessary for good growth otherwise your
substrate could foul. Under good conditions, plants grow rapidly and
their roots spread through the substrate and provide oxygen and draw
nutrients from the substrate. While there are some benefits to
providing a larger proportion of nutrients or a moderately higher
concentration in the substrate, it is impossible to prevent some of
those nutrients from making their way into your aquarium water. If
you're careful, this won't become a problem but don't overdo iron
additions to your water or it will turn green.
I don't see any reason to recommend to anyone constructing a plant
tank to use an undergravel filter (unless you intend to perform some
kind of controlled experiment with multiple tanks). Such devices
interfere with natural biological processes which occur in the
substrate below about 1/2" where the lack of oxygen allows anaerobic
bacteria to reduce iron compounds to the more soluble ferrous state.
This condition also favors availability of nitrogen, phosphorus and
manganese nutrients within the substrate.
I prefer to use high light intensities in order to ensure that my
plants can produce sufficient oxygen for my fish and to keep the
substrate sweet. Under these conditions, you need to supply CO2 or
else you will get pH soaring to +10 because the plants will resort to
utilizing carbonates. You also tend to get nutrient deficiency
symptoms much quicker; but plants grow faster and bigger too.
Under moderate lighting conditions (2wpg), one must ensure that the
organic material used is very, very well composted or you could have a
situation where the tank goes into oxygen deficit. That would sour
your substrate and cause problems for some fish which require high
oxygen concentrations. Note that many kinds of fish such as our Amazon
natives like catfish and neons normally live in lower oxygen
concentrations. Specific types of peat may be useable since the acidic
content will prevent decay.
Under lower lighting conditions (1wpg or less), you could probably
construct a soil or peat tank which required no CO2 injection. You
probably will not have oxygen saturation in such a tank and plants
should grow well but slowly with minimal algae problems.
I think its a wise precaution to use an iron supplement to the
substrate such as laterite (mostly iron oxides and hydroxides) or
micronized iron (which you can find in gardening stores).
Probably the best main component (90%) of your substrate should be
sand upto grain size 2-3 mm. You need at least 2-3 mm for the top
layer in order to get cuttings to stay in place and to prevent finer
components like laterite, soil or clay from mixing into the water.
Finer sand seems to be a good choice for the lower layers.
Steve P in Vancouver where Spring has Sprung!!