for the Planted Aquarium
Aquatic plants, water chemistry, and cichlids
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 that 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
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
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 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 suffer.
Another concern would be the buoyancy of the substrate, it 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 development.
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 affect, 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
disadvantages 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 available to the plants as the organic
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, proving 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 life span, so nutrients need to be replaced or
the substrate replaced.
RUGFs/UGFs (Reverse underground filters/underground filters) and
heating cables can manipulate the normal life span 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 life span by
making a more efficient bed, or a decrease of life span 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 the about the
same, higher flow rates having faster flows. Again, slow and gentle. Too
much flow may increase unwanted nutrient levels in the water column.
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 chucks for use in established tanks. Has relatively low CEC.
Zeolite - any of various hydrous silicates of aluminum that are
analogous in composition to the feldspars. Contains either sodium or
calcium or both of the type Na2O2.Al2O3.xSiO2.xH2O. Can act as
ion-exchangers. Has high CEC.
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
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 fractured 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. Gray to yellow color.
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 exchangeable cations of a soil. As long as a
material has a measurable CEC, it should work well in an aquaria's fertile
The pH determination 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 grandular 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
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 organics matter; will
Finland pine/fir forest - Eno, Northern Carelia, Finland - sand and
silt; beige-orange; homogenized; small amount of organics; will cloud
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
earth kiln fired to ceramic grandules; 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 organics 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 matter.
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 grandules; 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
Flourite - Seachem, USA - fracted, stable clay; very hard;
multi-colored (brown, red-brown, black); resembles aquarium gravel; no
South Carolina topsoil - South Carolina, USA - sand and silt; large
amounts of dark humus; soft and powdery; orange-brown; will float and
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
Onyx Gravel - Seachem, USA - naturally source fracted substance;
appears to be porous clay or rock; very hard; light and dark grey;
resemvles 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
here SUBSTRATE DATA CHART click here
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 mineral content.
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, even
though 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 surprise can from the CaribSea Laterite, which posted an
even higher pH of 9.8. It does not seem to contain any calcium carbonate
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.