NEWS113
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many fishes and proper maintenance of
some species isn'tpossibleat all unlessat
least part of the bottom is covered in
sand.
A major disadvantage of sand is that a
very large number of plants won't grow
properly in a sand substrate. This is
because sand becomes relatively close-
packed and allows comparatively little
water circulation. Plus not very much
organicmaterial (mulm, i.e. the excreta of
the fishes and dead plant debris)
penetrates into sand. The result is a
shortageof nutrients in the substrateand
that in turn leads topoorplantgrowth.Of
course that can be countered by using a
layer of substrate containing nutrients
beneath the layer of sand.But in that case
youmust always make sure that digging
fishes cannot reach this lower layer, as
otherwise the result will be serious
cloudingof thewater.
Sand (and the same applies to gravel,
below)naturallycontains "dirt", inpractice
amixtureof very fine sandandclay.This is
the last thing you want in the aquarium,
and so it shouldn't be left in the sand, as
otherwise if youhavedigging fishes in the
aquarium thewaterwill alwaysbe cloudy.
In addition unwashed sand containing a
lot of dirt is inclined to become
compacted (see above). Hence before
sand is used in the aquarium it shouldbe
washed until the water in the bucket
remains clear even when the sand is
stirredvigorously.This is a rather tiresome
business!
Gravel - theuniversal substrate
Gravel is the termused for agrain sizeof 2
mm to6cm. In theaquariumgravelwitha
grain sizeof 3-5mm isgenerally regarded
as the universal substrate. It is loose
enough for mulm to sink into it and the
water can circulate adequately, but it is
also close-packed enough for the roots
the plants to find a good hold. Gravel of
this grain size again usually contains dirt.
Nevertheless it doesn't normally need to
bewashed thoroughly.Thedirtmaycloud
the water somewhat initially, but the
cloudiness soon disappears as the
particles sinkback into thegravel.Thisdirt
is exceptionallygood for promotingplant
growth. It acts as a catalyst for numerous
nutrients that plants take up via their
roots. However, anyone who wants to
keep fishes that dig a lot will have to
dispensewith the beneficial effect of the
dirt and wash the gravel thoroughly
before using it in the aquarium. It should
bementioned that thecloudinesshasone
major drawback: the particles also settle
on the leaves of plants,which doesn't do
them any good at all. For this reason
particularly delicate, fine-leaved plants
(Myriophyllum,Cabomba,Limnophila,etc)
shouldn't be planted until aweek or two
after a new aquarium is filled, when the
water is completely crystal clear.
Structureof the substrate
The following structuringof the substrate
is recommended for the vast majority of
aquaria: a relatively small area in the
foreground of the aquarium - at most a
quarter of the entire bottom area - is
coveredwith a 2-3 cm thick layer of well-
washed sand.This sandyarea is separated
from the background using suitable
stones to create a terrace,which is infilled
to a depth of 4-5 cm with unwashed
gravelwithagrain sizeof 3-5mm topped
witha2-3 cm thick layer ofwashedgravel
of the same grain size. The sandy area is
left unplanted and serves as a ”play-
ground” for sand-loving fishes. If this
sandyareasubsequently looks toobarren,
pieces of bark or stones, with aquatic
mosses, Java Fern, or Anubias attached,
canbeplaced there.Thebackgroundarea
can be planted with the complete range
of available aquatic plants that will thrive
under the lighting and water conditions
prevailing in theaquarium inquestion.
Substrateadditives
The fertilization of aquarium plants
usually takes place via the water, and
experience has shown that this method
works very well. There are, however,
sensible additions to the substrate that
encourageoptimal plant growth.
Pre-fertilized substrate
Several manufacturers offer substrate
materials with a long-term fertilizing
effect. The plant nutrients in this type of
substrate are designed to be released
slowly into the water. They are advisable
for use where the primary intention is to
have themost luxuriantplantedaquarium
possible,with swordplants (Echinodorus),
crypts (Cryptocoryne), dwarf waterlilies
Biotope photo from French Guiana, with an "earth-eater" of the species
Satanoperca rhynchitis
in the
center of thepicture.Even in thewild the sandybottom - ashere - isusuallyplant-free.
