Substrates for the Planted Aquarium
There are a wide variety of substrates for use in today's planted
aquarium. Due to the growth and popularity of aquatic plants, new products
are being introduced all the time. This is good for us gardeners, but it
only adds to the confusion of which type is best. These new varieties, along
with the old standards, has given us many different choices. Some
people stick with the proven recipes, while others experiment with new
and sometimes untested ideas. A lot of real world data exists to substantiate
the viability of commercial substrates and additives, as well as homemade
peat, vermiculite, or soil blends. It's all up to the needs of the individual
aquarist. Some like the simplicity of commercial products while others
enjoy preparing the substrate they believe to be most productive.
No single substrate can be labeled as the best, but there are
ones which perform better than others. Many factors affect the type of
substrate needed: types of plants, appearance, growth rate, maintenance,
inhabitants, chemical properties, budget, and availability. As you can
see, there are several parameters that go into deciding the optimal substrate. The purpose of this substrate analysis and overview is to help narrow down some of those parameters, especially the physical and chemical properties.
The substrate serves many different purposes in the planted
tank, probably more than in any other type of aquaria. It provides a place
where mineral and organic nutrients are stored. These nutrients are released
to root-feeding plants as needed. It also provides a bed for the growth
of beneficial bacteria. These bacteria are responsible for breaking down
wastes. They also are responsible for the mechanisms that cause reduction
reactions on the nutrients, making them available for uptake by the plants.
Iron, along with other nutrients, needs to be in the reduced state to be
utilized by the plants. Reduction turns the commonly found ferric iron
(Fe+3) into ferrous iron (Fe+2). The negatively charged sites of the substrate
attract and hold the positive ions until needed by the plant's roots.
The bacteria also breakdown fish and plant wastes, as well as
extra food. When new tanks are set up, the bacteria are just beginning
to establish themselves and this is usually what causes the phenomenon
"new tank syndrome". The aquarist may experience high ammonia and nitrite
spikes until the tank settles in. It may be beneficial to seed your new
tank with some gravel from another trustworthy tank. This will give the
bacteria a jump start.
As well as being a good anchoring medium, a substrate must be
aesthetically pleasing. Fish and plant colors will appear more deep and
rich with a dark substrate. This is a good look for a soft water, Amazonian
aquascape. A tank with a top layer of sand usually resembles a shallow
shoal, bright and alive. Fish may be more timid with the washed-out bottom
Commercial, as well as prepared substrates, must have the correct
size granules. Too large and waste will settle down deep, clogging the
substrate from nutrient exchange. Too small and it might have the tendency
to settle and compact. A compacted substrate will not allow for the growth
of small, delicate roots. It would also impede the flow of nutrients throughout
the bed. Eventually, in both cases, growth would slow and your plants would
Another concern would be the bouyancy of the substrate. They should
sink and stay sunk. If not, cover with a top dressing of sand or gravel.
Materials like pumice, peat, humus, and vermiculite tend to float if given
the chance. Boiling these before application will saturate them, helping
keep them controllable until covering.
Try to avoid using fine-granulated sands. Choose the largest
grade available. Beach sand should also be avoided. Gravel size should
be 2-5mm, and luckily these are the most popular sizes. The gravel and
sand need to be chemically inert. This will insure the pH and other water
parameters aren't affected by the substrate. Before application, add a
drop of hydrochloric acid to the material in question. If it fizzes or
foams, do not use it, or be aware it may alter your water chemistry.
Sand and gravel need to be washed thoroughly before use to
remove the dust and trash. Make sure your substrate does not contain shells.
They will increase the hardness and alkalinity over time. If a commercial
product is being used, follow their preparation instructions. You can even
experiment, there are endless possibilities.
Calcined clays, lateric rock, and zeolite, can be used as complete
substrate beds or mixed up to fifty percent with other products. Plain
gravel makes a good mixer, but should be avoided as a stand-along substrate.
Be sure to thoroughly rinse these products, they can contain a large amount
of fine dust that can initially cloud the water and settle on your plants. Lateric soils, redart clays, and soils need to be mixed with gravel and
put in the lower third of the substrate. These types cannot be rinsed before-hand,
and will easily mix into the water column if left too close to the surface.
Collected soils need to be sterilized in an oven at 200ºF for one hour and
then sifted to provide the highest quality soil. Be careful not to collect
near heavily traveled areas or areas that could be easily contaminated.
Aquariums are closed systems, so quality is paramount. Peat, vermiculite,
and other additives would also be mixed in the lower layer. Cover the lower
layers with a top layer of gravel or sand. You are now ready to plant.
Tanks are most appealing if the substrate is terraced from back
to front. A minimum depth of 3" in the front to a minimum of 5-6" in the
back is best. This allows for the entire surface of the substrate to be
viewed, from the small foreground plants (glosso and chain swords) to the
larger, heavy feeders (swords and crypts). It's up to the individual to
decide on the final look, but remember to provide a good depth for root
If substrate heating cables are going to be used, a small base
(1/2-1") is applied for the cables to rest on. They need to be placed in
the correct orientation for the optimal effect, flat with clearance on
all sides. Cover and complete the substrate as normal.
Regardless of what substrate you decide on, problems can
arise. They maybe built-in problems, too rich or organic, or they may gradually
appear, low in nutrients or compactness. The built-in problems can be controlled,
to an extent. Peat, manure, leaf debris; all can be used, but in moderate
amounts. With the advances in today's fertilizers, manure's disadvantanges
may outweigh it's advantages. Peat and leaf debris also decompose to form
noxious, low pH environments. Laterites and clays are rich in minerals,
but not organics. These minerals are stored within the substrate and are
not as readily availible to the plants as the organics are. High mineral
concentrations rarely cause problems, but the absence of certain ones will.
Too little or too much of anything is bad. That's why it's important to
be aware what minerals are present and in what concentration. Nutrients
can be amended to the substrate to correct deficiencies. Clay balls can
be moistened and baked at 250ºF until hard, then inserted under the plants
that show problems or are heavy feeders. Mulm can't always provide the
nutrients needed for a fast-growing tank, but time-released fertilizers
(Osmocote) or plant spike (Jobes) can keep things in balance. They need
to be low in phosphorus (middle number of N-P-K), as not to promote algae
growth if leached from the substrate.
Compactness may be experienced somewhere down the road for an
aged tank. The plant roots alone could amass to cause problems, on top
of physical compacting. Vacuuming the gravel LIGHTLY will help to prevent
compactness. It will also give the tank a cleaner appearance. Care must
be taken not to disturb additives or fertilizers. Mulm is removed and more
oxygen is supplied to the roots. Vacuuming is another one of those individual
decisions. There are good arguments on both sides. Some people allow the
fish and food wastes to remain, providing food for snails, bacteria, and
plants. However, a clogged substrate is not a healthy substrate, so a periodic
light vacuuming may not be a bad idea. Most problems can be resolved
before a total breakdown is needed.
As with most things, there is a break-in period for substrates.
Newly planted tanks may take a few weeks or several months to become stable.
Ammonium, nitrite, and nitrate levels will bounce around until the bacteria
are established. They will allow more nutrients to become available to
the plants. The plants will then start establishing themselves and a balanced
tank can be achieved. As with potted house plants, the nutrients can become
exhausted over a period of time. The planted aquarium also has a lifespan,
so nutrients need to be replaced or the substrate replaced.
RUGFs/UGFs (Reverse underground filters/underground filters)
and heating cables can manipulate the normal lifespan of the substrate.
They cause a greater flow of nutrient water through the bed, improving
nutrient exchange rates. It is not known if this causes an increase of
lifespan by making a more efficient bed, or a decrease of lifespan by using
up the nutrients more rapidly. A thousand arguments have been raised and
debated, but it's still up to the aquarist. Heating cables can be used
with most substrate choices, but RUGFs/UGFs need to be used with hard,
calcined clays or lateric rock only. Heating cable flow is determined by
the amount of heat being used, hotter causing faster flows. The right wattage
should be used to get a slow, gentle flow. Underground filters are about the same, higher flow rates having faster flows. Again, slow and
gentle is preferred. Too much flow may increase unwanted nutrient levels in the water
Gravel - pH-inert, natural or epoxy-coated. Loose rounded fragments
of rock. Usually >2mm in size. Most gravels have no nutrient or CEC value. Gravels are cheap and have good anchoring properties.
Sand - sediment particles. Most common form is silicon dioxide (SiO2).
Size 0.05-2mm. No nutrient or CEC value. pH-inert.
Laterite - a low-grade ore similar to bauxite, but containing much
less aluminum oxide (Al2O3). A residual product of rock decay. Usually
highly weathered tropical clay with high concentrations of iron oxides
and aluminum hydroxides. Comes in powder/granular form, used in new set-ups,
and chunks for use in established tanks. Has relatively low CEC.
Zeolite - any of various hydrous silicates of aluminum that are analogous in compostion to the feldspars. Contains either sodium or calcium or both
of the type Na2O2.Al2O3.xSiO2.xH2O. Can act as ion-exchangers. Has high
Arcillite - calcined, montmorillonite clay.
Montmorillonite - one of the major components of bentonite and fuller's earth. Hydrous aluminum silicate with a considerable capacity for exchanging part of the aluminum for Mg and bases. High natural adsorptive power. Good CEC.
Redart clay - high in iron. It has similar properties of laterite, i.e
iron content and CEC, but it is not a laterite. It's usually finely ground.
Peat - semicarbonized residue of plants formed in watery environments. High organic content. When added to water, tannins are released and acidic water is formed. Can absorb hardness from water column. High CEC.
Vermiculite - micaceous material. Hydrated magnesium-iron-aluminum silicates resulting from expansion of granules of mica at high temperatures. This gives a lightweight, highly water-absorbent material. Crystalline structure. High CEC.
Soil - consists of inorganic matter derived from weathered rocks and organic matter from decayed vegetation. Those with 45-50% sand 20-28% clay are called loams. Those >50% sand are called sandy and those with >28%
clay are in the clay group. Varying CEC.
Clay - hydrated aluminum silicates and other minerals. Generalized
formula of Al2O3SiO2.xH2O. Component of soils in varying percentages. Fine
irregular shaped crystals from 150 microns to <1 micron (colloidal).
Reddish-brown to pale, depending on iron content. Absorbs water, plastic
when moist, hard when fired, can be thixotropic (property of various gels
of becoming fluids when disturbed). Good CEC.
Calcined clays - clays that are heated to a high temperature to cause an extreme hardening and oxidation. They can then be fracted into smaller
pieces to be used as a primary substrate base. They become very porous
on firing, and provide many nutrient binding sites. Chemically and physically
stable. Good CEC.
Illite - group of clay minerals having the structure KAl3Si3O10(OH)2. Colorless to pale brown potassium mica. High CEC.
Mica - any of several silicates of varying chemical composition but
with similar physical properties and crystalline structures. All cleave
into thin sheets that are flexible and elastic. Good CEC.
Bentonite - colloidal clay of aluminum silicate compound. Composed chiefly of montmorillonite. Two types: sodium bentonite (Western US) has high swelling capacity with water and calcium bentonite (Southern US) has negligible
swelling capacity. Forms colloidal suspensions in water with strong thixotropic
properties. Good CEC.
Fuller's earth - porous, colloidal aluminum silicate clay mineral that
lacks plasticity and is often used as an adsorbent, filter medium, and
a carrier for catalysts. High adsorptive power. Grey to yellow color. Good
Ceramic - a product manufactured by the action of heat on earthy raw materials, in which silicon and its oxide and complex compounds known as
silicates, occupy a predominate position within the material. Varying CEC.
All testing was done by one analyst. All samples were analyzed
on the same instruments and testing took approximately one week to complete.
This was important, since methodologies used by individuals may vary. I
initiated the research with a request for testing materials via The Aquatic
Plants Digest. I had several substrates of my own to start, but tested a total of 25, consisting of commercial products, local soils/clays, and homemade blends. I feel
it is a very good representation of what's available.
Testing consisted of soil pH's, total leachable metals, and
cation exchange capacity (CEC). Soil pH is important because it can show
the chemical possibilities of your substrate. It's chemical properties
could alter the surrounding water column. That is not the same for the
total metals. These analytes are bound in the crystalline structures. Materials
release their metals at different rates, depending on the make-up. The
hard, calcined clays have the ability to retain nutrients longer than the
soft, moldable clays.
The CEC determination helps us gardeners know which substances are
more efficient at nutrient binding. CEC is a reversible chemical reaction
between a solid and a fluid in which ions may be interchanged from one
substance to another. The values are expressed in milliequivalents per
100g and are the total sum of exchangable cations of a soil. As long as
a material has a measurable CEC, it should work well in an aquaria's fertile
The pH detemination was done with equal amounts of soil and
deionized water. The samples were shaken to mix thoroughly and allowed
to settle before testing. Testing was done with an Orion 720A pH/Conductivity
meter. The total metals were analyzed on an inductive coupled plasma
(ICP) instrument. Acid digestion of the samples was done according to EPA
SW-846 Method 3050A. The CEC determinations were done by Method 9081A of
EPA SW-846. CEC extractions were also analyzed on the ICP. Samples were
all analyzed in their original forms. Care was taken to analyze them as
they would be utilized by the aquarist. Note that crushing would increase
the surface area and may change the parameter values given here.
Substrate Gold - Schoeler Enterprises, USA - lateric soil mined
in the US; comes in granular and stick forms; deep, orange-red; silt-5mm
in size; no organic matter; will cloud water.
Yolo loam/vermiculite - Yolo County, CA, USA - local loam/vermiculite
blend; unknown percentages of ingredients; homogenized; shiny, brown, mica appearance; very small amount of organic matter; will cloud water.
Danish redart clay - Danish pottery, Denmark - powdery; brick red dust; no organic matter; will cloud water.
Finland local clay - Viikki, Helsinki, Finland - silty; dusty; light-beige;
silt-5mm in size; easily crumbled; no organic matter; will cloud water.
Finland pine/fir forest - Eno, Northern Carelia, Finland - sand and
silt; beige-orange; homogenized; small amount of organics; will cloud water.
Finland mixed forest - Helsinki, Finland - sand and silt; powdery; brown; will cloud water.
First Layer Pure Laterite - Aquarium Pharmaceuticals, USA - hard lateric soil and rock; mining location unknown, possibly US; deep, brown-red; <1-5mm in size; no organic matter; will cloud water.
Profile - Profile Products LLC/Shultz, USA - illite and fuller's earth
kiln fired to ceramic granules; dark grey with beige specks; 1mm in size;
no organic matter.
Ontario preglacial subsoil - Don River Valley Brickworks, Toronto, Canada - powdery with small rocks; light grey; homogenized; silt-5mm in size;
no organic matter; will cloud water.
Ontario postglacial topsoil - mixed hardwood lot, Don River Valley,
Toronto, Canada - sand and silt; dark grey-brown; homogenized; some organic
matter; will cloud water.
Terralit - Aqualine Buschke, Germany - zeolite-based; very hard; multi-colored (white, brick red, black); resembles small aquarium gravel; 2-5mm in size; no organic matter.
AquaTerra - Natural Aquarium and Terrarium, USA - powdery, highly organic blend, possibly peat and laterite; dark red-brown; homogenized; will float
and cloud water.
Hartz pH 5 cat litter - Hartz, USA - possibly type of arcillite; hard,
will not break down in water; light beige to cream; 1-3mm in size; no organic
Cedar Heights redart clay - Resco, USA - powdery; brick red dust; no organic matter; will cloud water.
Dupralit G - Dupla, Germany - lateritic soil commonly mined in Sri Lanka; deep orange-red; silt-2mm in size, some larger granules; very small amount of organic matter; will cloud water.
Turface - Profile Products LLC, USA - medium hard arcillite and other
clays, possibly kiln fired; light beige; resembles aquarium gravel; 2-5mm
in size; no organic matter.
Turface (black) - Profile Products LLC, USA - medium hard arcillite and other clays, possibly kiln fired; dark brown and black; resembles aquarium
gravel; 2-5mm in size; no organic matter.
Greensand - (manufacturer unknown) - substrate additive; medium hard, will crumble, dark green; silt-1mm in size; small amount of organic matter;
some matter will float and cloud water.
Special Kitty cat litter - Walmart, USA - soft, crushable clay pieces;
possibly bentonite and montmorillonite; light grey; 2-5mm in size; no organic
matter; will cloud water.
Natural River Rock - (manufacturer unknown) - very hard calcined clay; light beige; resembles aquarium gravel; 2-5mm in size; no organic matter.
Flourite - Seachem, USA - fracted, stable clay; very hard; multi-colored (brown, red-brown, black); resembles aquarium gravel; no organic matter.
South Carolina topsoil - South Carolina, USA - sand and silt; large
amounts of dark humus; soft and powdery; orange-brown; will float and cloud
Play sand - Lowes, USA - clean, no visible trash; white and clear; 1mm in size; no organic matter.
CaribSea Tropic Isle Laterite - CaribSea, USA - very hard lateric rock; deep brown-red; resembles large aquarium gravel; 2-10mm in size; no organic matter.
Onyx Gravel - Seachem, USA - naturally source fracted substance; appears to be porous clay or rock; very hard; light and dark grey; resembles large aquarium gravel; 2-10mm in size; no organic matter.
Tetra Initial Sticks - Tetra Products - substrate additive; medium hard, will crumble; dark grey; 5-10mm pellets; good amount of organic matter;
will float and cloud water.
India local laterite - Northern Nune, India - powdery; deep brick red; silt-2mm in size; very small amount of organic matter; will cloud water.
Aquatic plants demand a good supply of iron for proper development.
The search for iron sometimes decides what substrate choices we make. Macronutrients like calcium, magnesium, and potassium are also important in plant growth. Zinc, copper, manganese, etc. must be present in small amounts to provide
essential micronutrients. First Layer Laterite has the highest amount of
iron, a strong 11.8%. The local Indian laterite was right behind, with
11.4%. These values are a good approximation of total amounts. All the
lateric soils have good iron content. The redart and natural clays had
medium iron content. All other had medium to low amounts. If iron levels
are low in your substrate, just amend it with clay or laterite balls. The
Yolo loam/vermiculite blend has got to get an honorable mention for total
A neutral to acidic substrate is the preference for the majority
of aquarists. An important thing to remember, most bacteria are most productive
at a pH of approximately 5.5. Macronutrients are best utilized by the plants
at a neutral pH, while micronutrients are best at low pHs. The two redart
clays had alkaline pH's and were comparably similar, eventhough a world
apart. The preglacial Ontario clay had a large amount of calcium carbonate
(CaCO3) and it's pH corresponds to this. It was very different from the
Finish clay, which resembled it in color and composition. The Onyx gravel
reinforced it's buffering claim with a high pH, but the big suprise came
from the CaribSea Laterite, which posted an even higher pH of 9.8. It does
not seem to contain any calcium carbonate (CaCO3).
The organic matter present in some of the samples would seem
to dictate low pH values, and that is exactly what was found. The Tetra
Initial Sticks had the lowest pH. They would work on new set-ups
by getting an acidic bed started, allowing for a quicker exchange of nutrients.
Nitrifying bacteria work better in these low pH environments. AquaTerra
also contained a large amount of organic matter, and it was a close second
to the Tetra Sticks. All other samples had pretty common pH values.
Cation Exchange Capacity (CEC)
Some gardeners swear by CEC values, while others grow aquatic
plants with nothing but blind faith. It is interesting to know the actual
parameters of each substrate, but I've seen plants grown in plain sand
and gravel. The samples that lacked at least some organic matter or clay,
had slightly lower CECs. The big surprises here were Terralit and Tetra
Initial Sticks. The zeolite composition of Terralit provides an excellent
ion exchanging medium and has good mineral concentrations. The Tetra Sticks,
with it's high organic and mineral content, also had a high CEC. The sandy
samples had very poor CECs.
The longer you look at the data tables, the more observations
you begin to notice. I think the data has provided the aquatic gardening
community an invaluable source of knowledge. Hopefully it can help narrow
the decision making and clear up some of the confusion associated with
I hope this analysis and overview has provided a good starting
point for a successful planted aquarium. Regardless of data or arguments,
it is still up to the individual to decide what's best for their needs.
I have grown plants in sand, gravel, Flourite, and litter. All substrates
gave good growth, given all other parameters were optimal. It's true some
were more attractive, had higher iron levels, or contained more organic
matter, but all can be utilized if set up and maintained properly.
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