Cec Of Calcined Montmorillonite

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Science for Aquarists

Substrates for the Planted Aquarium

Jamie S. Johnson

There is a wide varity 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 over which product is best. These new varieties, along with old standards, have given us many choices.

Some people stick with proven recipes, while others experiment with new, and sometimes untested, ideas. A lot of real world data exists to substantiate the value of commercial substrates and additives, as well as homemade peat, vermiculite, and 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 is most productive.

No single substrate can be labeled as the best, but some perform better than others. Many factors affect the type of substrate needed: types of plants, appearance, and growth rate desired; maintenance one will tolerate; chemical properties; budget; and availability. As you can see, there are many 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 physical and chemical properties.


The substrate serves many purposes in the planted tank— probably more than in any other type of aquarium. 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.

Bacteria also cause reduction of nutrients, making them available for uptake by the plants. Iron, along with other nutrients, needs to be in the reduced state to be used by plants. Reduction turns the common oxidized ferric iron (Fe+3) into ferrous iron (Fe+2). The negatively charged sites in the substrate attract and hold the positive ions until taken up by the plant's roots.

Bacteria also break down fish and plant wastes and excess food. When new tanks are set up, bacteria are just beginning to establish themselves. This is usually what causes the phenomenon "new tank syndrome". The aquarist may experience high ammonia and nitrite spikes until the tank stabilizes. It may be beneficial to seed your new tank with some gravel from another trustworthy tank. This will give the bacteria a jumpstart.

As well as being a good anchoring medium, a substrate must be aesthetically pleasing. Fish and plant colors will appear deeper and richer with a dark substrate. This is a good choice 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 a washed-out colored bottom.

Commercial and homemade substrates must have correct size granules. If the particles are too large, waste will settle down deep, clogging the substrate and inhibiting nutrient exchange. If the particles are too small, the substrate may settle and compact. A compacted substrate will not allow for the growth of small, delicate roots. It also impedes the flow of nutrients throughout the bed. Eventually, in both cases, growth slows and plants suffer.

Consider the buoyancy of the substrate; it should sink and stay sunk. If it doesn't, cover it 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 use tends to saturate them, helping them stay down until covered.

Try to avoid using fine-grained sands, such as beach sand. Choose the largest grade available. Gravel size should be 2 to 5mm; fortunately, 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.


If you use a commercial product, follow preparation instructions. Wash sand and gravel thoroughly before use to remove dust and trash. Thoroughly rinse these products because they can contain a lot of fine dust that can initially cloud the water and settle on your plants.

If your substrate contains shells, it will increase the hardness and alkalinity over time. Be sure to include this effect in your aquarium management plan.

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-alone substrate. 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 beforehand, and will easily mix into the water column if left too close to the surface.

Collected soils can be sterilized in an oven at 300F 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 three inches in the front to a minimum of five to six inches 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 sufficient material for proper root development.

If you use substrate heating cables, you need a small base (0.5 to 1 inch) for the cables to rest on. Place the cables in the correct layout for optimal effect: flat with clearance on all sides. Cover and complete the substrate as normal.


Regardless of the substrate you choose, problems can arise. They may be built-in problems (too rich or organic) or they may gradually appear (lack of nutrients or compacting). The built-in problems can be controlled, to an extent. You can use peat, manure, or leaf debris in moderate amounts. With the advances in today's fertilizers, manure's disadvantages may outweigh its advantages. Peat and leaf debris decompose to form noxious, low pH environments. Laterites and clays are rich in minerals but not in organics. These minerals are stored within the substrate and are not as readily available to the plants as the organics.

High mineral concentrations rarely cause problems, but lack of certain minerals may. Too little or too much of anything is bad. That's why it's important to know what minerals are present and in what concentration. You can add nutrients to the substrate to correct deficiencies. You can moisten clay balls and bake them at 250oF until hard, then insert them 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 spikes (Jobes) can keep things in balance. They need to be low in phosphorus (middle number of N-P-K), so they won't promote algae growth if leached from the substrate.

As time goes on, your substrate may compact. The plant roots alone can amass, causing problems in addition to physical compacting. Vacuuming the gravel lightly will help to prevent compaction and 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

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Substrate Types/Additives

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; common form is silicon dioxide (SiO2); size 0.05 to 2 mm; no nutrient or CEC value; pH-inert.

Laterite - a low-grade ore similar to bauxite, but containing much less aluminum oxide (Al2O3); 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; 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-exchanger; has high CEC.

Arcillite - calcined, montmorillonite clay, this may be a commercial brand name.

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; similar iron content and CEC to laterite (but not a laterite): usually finely ground.

Peat - semicarbonized residue of plants formed in watery environments; high organic content; releases tannins when wetted, forms acidic water; can absorb calcium from water column; high CEC.

Vermiculite - micaceous material; hydrated magnesium-iron-aluminum silicates resulting from expansion of granules of mica at high temperatures; lightweight, highly water-absorbent material; crystalline structure; high CEC.

Soil - inorganic matter derived from weathered rocks and organic matter from decayed vegetation; if 45 to 50% sand, 20 to 28% clay called loam; if >50% sand called sandy; if >28% clay called clayey; 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 <1 micron (colloidal) to 150 microns; 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; can be crushed into smaller pieces to be used as a primary substrate base; very porous upon 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; cleaves into thin, flexible and elastic sheets; good CEC.

Bentonite - colloidal clay of aluminum silicate compound; composed chiefly of montmoril-lonite; sodium bentonite (western US), high swelling capacity with water; calcium bentonite (southern US), 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, carrier for catalysts; high adsorptive power; gray to yellow color; good CEC.

Ceramic - a product manufactured by heat acting 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.

Sample Descriptions

Substrate Cons

1. 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

2. 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

3. Danish redart clay - Danish pottery, Denmark -powdery; brick red dust; no organic matter; will cloud water

4. Finland local clay - Viikki, Helsinki, Finland -silty; dusty; light-beige; silt-5mm in size; easily crumbled; no organics matter; will cloud water

5. Finland pine/fir forest - Eno, Northern Carelia, Finland - sand and silt; beige-orange; homogenized; small amount of organics; will cloud water.

6. Finland mixed forest - Helsinki, Finland - sand and silt; powdery; brown; will cloud water

7. First Layer Pure Laterite - Aquarium Pharmaceuticals, USA - hard lateric soil and rock; mining location unknown, possibly US; deep, brown-red; <1 to 5mm in size; no organic matter; will cloud water

8. Profile - Profile Products LLC/Shultz, USA - illite and fuller earth kiln-fired to ceramic granules; dark gray with beige specks; 1mm; no organic matter; this is the older, "fine" formulation.

9. Ontario preglacial subsoil - Don River Valley Brickworks, Toronto, Canada - powdery with small rocks; light gray; homogenized; silt-5mm in size; no organics matter; will cloud water

10. Ontario postglacial topsoil - mixed hardwood lot, Don River Valley, Toronto, Canada - sand and silt; dark gray-brown; homogenized; some organic matter; will cloud water

11. 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

12. AquaTerra - Natural Aquarium and Terrarium, USA -powdery, highly organic blend—possibly peat and laterite; dark red-brown; homogenized; will float and cloud water

13. 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

14. Cedar Heights redart clay - Resco, USA - powdery; brick-red dust; no organic matter; will cloud water

15. Dupralit G - Dupla, Germany - lateric soil commonly mined in Sri Lanka; deep orange-red; silt-2mm in size with some larger granules; very small amount of organic matter; will cloud water

16. Turface - Profile Products LLC, USA - medium hard


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