Gravel in a freshwater aquarium
The substrate of an
aquarium refers to the material used on the tank bottom.
It can affect water chemistry, filtration, and the
well-being of the aquarium's inhabitants, and is also an
important part of the aquarium's aesthetic appeal. The
appropriate substrate depends on the type of aquarium; the
most important parameter is whether the aquarium contains
fresh water or saltwater.
Substrates for freshwater aquaria
For
freshwater aquaria, gravel is the most common substrate.
Gravel sold specifically for use in aquaria is chemically
inert. It may be naturally colored or dyed, and may have a
polymer seal to ensure it does not affect water chemistry.
Types of substrates for freshwater include the following:
- Gravel. Aquarium gravel can be as coarse as
pea-sized or as fine as 1–2
mm. It is commonly composed of quartz or other
lime-free minerals.
[1][2]
- Shell grit, crushed
limestone, crushed marble or crushed coral skeletons. Because
calcium carbonate, the primary component of these
substrates, increases water hardness and pH, it is used
most often for particularly for hard water species, such
as those for African rift lake cichlids or cichlids from
Central America. Calcium carbonate substrates are
poorly suited to aquaria housing most other freshwater
aquarium fish, particularly river species, which are
adapted to soft water.
[2]
- Peat, or decomposed plant matter.
Peat is used most commonly in soft water or blackwater
river systems, such as those mimicking the Amazon River
basin. In addition to being soft in texture and
therefore suitable for demersal (bottom-dwelling)
species such as Corydoras catfish, peat is reported to
have a number of other beneficial functions in
freshwater aquaria. It softens water by acting as an ion
exchanger, it contains substances good for plants and
for the reproductive health of fishes, and can even
prevent algae growth and kill microorganisms. Peat often
stains the water yellow or brown due to the leaching of
tannins.
[2]
- Sand. This is often recommended for use with
certain species, such as the river stingrays of family
Potamotrygonidae, which bury themselves in the fine
substrate. However, these species can be successfully
kept with coarser substrates as well.
In some aquaria, different substrates are used in
different parts of the tank. For example, peat can be used
in one corner, while gravel in another portion allows rooted
plants.
[2]
Freshwater aquaria with live
plants
Planted tanks require a substrate that will remain
loose enough for plant roots to penetrate it. The substrate
should be chemically inert and free of sharp edges. Examples
include sand and gravel; fine gravel (1–2 mm) is preferred
by some aquarists because coarser substrates allow debris to
settle within the gaps between grains, which is particularly
difficult to clean in a planted aquarium. Sloping the
substrate so it is most shallow in front accommodates larger
plants with correspondingly larger root systems in the back.
The substrate for plants should be at least 5 cm (2 in) deep. Often, a lower layer of richer substrate such as
potting soil, peat, vermiculite, or certain types of clay
are used as a source of iron and trace elements for plant
roots.[3][2]
Substrates for saltwater aquaria
For
saltwater aquaria, coral gravel and coral sand are most
common. Composed primarily of calcium carbonate, coral
skeletons have a buffering effect on the water's pH.
They also contribute calcium, needed by some invertebrates,
to the water.
In a
reef aquarium, the substrate can be an important part of
managing the water chemistry. Calcium carbonate substrates
such as those made from coral or oolitic aragonite are
commonly used; when these minerals, insoluble in water, are
dissolved by acid secretions, they release calcium and
strontium, both of which are important to invertebrates
such as stony corals.
Coral sand is considered the best substrate for a reef
aquarium. At a depth of about 2.5 cm (1 in), it allows
anoxic zones to form and host anaerobic bacteria which in
turn denitrify the water, that is, convert nitrate to
nitrogen gas. Animals such as sleeper gobies and some
invertebrates such as turbo snails are useful to stir the sand.
Aquaria with marine invertebrates often incorporate
live rock, which can be considered part of the
substrate. Made of calcium carbonate, it has the same
effects on water chemistry as coral gravel and sand. It is
riddled with small holes and cavities which allow anoxic
zones to form.[4]
Substrates for specialty tanks
In breeding tanks for egg-scattering species, a
layer of marbles is sometimes used as a substrate, allowing
the eggs to fall into the gaps between the marbles where the
parents cannot eat them.[5]
Quarantine tanks (sometimes called hospital
tanks) often use no substrate at all. This assists in
keeping the aquarium as clean as possible.
[1]
Biological filtration via
substrate
Beneficial bacteria colonize all aquarium surfaces that
are exposed to aerated water. Because the numerous particles
have a high surface area, substrates are often employed in
biological filtration.
In an undergravel filter, substrate (most commonly
gravel or crushed coral) is placed on top of a grate
containing one or more uplift tubes. Water is pumped up the
tubes using either an air pump or small water pump, forcing
flow through the substrate and aerating the entire gravel
bed. Beneficial bacteria colonize the gravel bed and provide
biological filtration. Undergravel filters are most often
used in small aquaria, although they can be used in larger
systems.
Undergravel filters are not effective if the substrate
bed is uneven or if very fine substrates such as sand or
peat are used. In an uneven gravel bed, water will flow only
through the thin portions of the bed, leaving the more
heavily covered areas to become anoxic. Because of this,
animals that dig, such as cichlids, are best kept in an
aquarium using some other type of filtration.
Even without an undergravel filter, some nitrifying
bacteria are present on the surface of the substrate.
References
- ^
a b
Substrate Materials. The Tropical Tank.
Retrieved on
2006-05-02.
- ^
a b c d e
Scheurmann, Ines (1985). Natural Aquarium Handbook,
The, (trans. for Barron's Educational Series,
Hauppauge, New York: 2000), Munich, Germany: Gräfe &
Unzer GmbH.
-
^ Randall,
Karen.
A Look At Substrate. The Krib. Retrieved on
2006-06-08.
- ^
Delbeek, J. Charles, Julian Sprung (1994). Reef
Aquarium, The, Volume 1. Coconut Grove, Florida:
Ricordea Publishing.
-
^ S. Russell.
Breeding Zebrafish (Chapter 2). The Zebrafish
Book. Retrieved on
2006-05-02.