Aquarium Soil | Acquisition And Preparation Of Soil

Last updated on December 24th, 2022 at 11:05 am

Aquarium Soil is specially prepared soil. It is sometimes also called “clay”, implying the presence of nutrients in comparison with traditional soil. Unlike ordinary gravel and sand, the soil is an active substrate that affects the hydrochemical composition of water. It promotes the establishment of mild, slightly acidic pH and dGH values. Which are suitable for much freshwater tropical fish, shrimp and is an excellent medium for plant growth.

Aquarium soil

For example, nutrient uptake by most plants is significantly improved at a pH below 7. In addition, the soil serves as a medium for the development of a beneficial colony of bacteria that converts organic waste into plant nutrients, helping to maintain biological balance.

Soil Made By

Depending on the manufacturer, the soil can be made from special clay materials, natural pressed earth, materials of volcanic origin, rich in trace elements, and other nutrients. In a special manufacturing process, the material is given a granular shape. Depending on the specific purpose, the composition may include additives from fertilizers, activated carbon, and other substances.

The balls of soil are stable in size and lighter than gravel particles. Which makes it easier for plants to sink into the substrate during planting and to root them. The color usually ranges from brown to black. Soil is the primary substrate for professional aqua scaping. Unlike sand, it is perfect for modeling underwater terrain, especially when wet.

How Does Soil Change The Hydro Chemical Composition Of Water?

Soil is a so-called cation exchanger, it acidifies water (lowers pH) and decreases water hardness. When interacting with water, positively charged hydrogen ions (H +) are released. The higher the H + content in water, the more acidic it becomes. The positively charged hydrogen ions also interact with sodium carbonate ions to form carbonic acid. 

As a result, the carbonate or temporary hardness (KH) of the water also decreases. Since it depends on the content of bicarbonate anions – HCO3. In addition, the aquarium soil binds calcium and magnesium cations (Ca 2+, Mg2 +) from the water. Which determines the overall hardness (GH) of the water, thereby softening it.

Due to its ability to exchange cations, the soil retains (stores) important nutrients for aquarium plants and releases them when needed. In this situation, the exchange goes in a different direction. The roots of plants release hydrogen ions, which are exchanged in the soil with bound cations of nutrients. Such as ammonium and potassium. The released nutrient ions are then absorbed by the roots.

Related : Tips for Beginner Fish Aquarists | Dis-infect Your Aquarium

How Often To Renew The Soil?

The cation exchange capacity of the soil in an aquarium is limited to several years. Over time, the effect of lowering the pH and water hardness decreases. The service life depends on the properties of the water used. If raw hard water is used (high content of calcium and magnesium salts) or limestones are used in the decoration, the effectiveness of the soil decreases faster. 

If soft water is used, the service life is correspondingly increased. After 2-3 years, a complete replacement of the substrate or the use of special soil fertilizers will be required. If the soil has been additionally enriched with minerals. Then they are usually consumed depending on the number of plants, usually within a year.

The substrate serves not only as a decorative element of the aquarium. But also as an important part of the internal ecosystem. It is a place for the rooting of aquatic plants and habitats for beneficial nitrifying bacteria participating in the nitrogen cycle.

Which is especially important in the case of a bottom filter. In addition, some species of fish instinctively bury themselves in the ground in case of danger or under the influence of seasonal factors. Others feed exclusively at the bottom, sifting soil particles with their mouths in search of food. And still, others lay eggs directly on the substrate, making small pits in it.

Soil Option

There are a huge number of soil options, which can be conditionally divided into three main groups: natural, artificial, and soil.

NATURAL – sand, gravel, crushed and polished rocks. Everything is usually a natural substrate in rivers and lakes. To increase the attractiveness to buyers, natural soil can be coated with safe colored enamel, synthetic resins, etc.

ARTIFICIAL – made from several types of plastic or sintered glass, as well as from various polymeric materials. They can have properties such as color change over time, “chameleon” effect, plasticity, glow, etc. It is mainly used as a decoration.

THE SOIL Is a specialized soil rich in trace elements and other nutrients necessary for plant growth. Affects the hydrochemical composition of water. They are mainly used in natural aquariums.

Important “The type of soil is primarily selected based on the needs of fish and plants. And your desire to decorate the aquarium as brightly or in an original way as possible should recede into the background.

When choosing soil, attention should be paid to the following parameters. Effects on the hydrochemical composition of water, grain size (soil particles), and color.

Impact On The Hydro Chemical Composition Of Water

As well as natural elements of decoration, some types of natural soil can influence the hydrochemical composition of water. For example, dolomite or marble chips increase dGH, while anthracite-based substrates acidify the water. Artificial soils, as well as sand, crushed and polished granite, basalt, quartz, and others, have neutral properties. 

Aquarium soil tends to acidify and soften the water, making it ideal for most plants to grow.
For example, you should not use a substrate of marble chips (increases dGH) when keeping Betta fish, gourami, most tetras, zebrafish, and others. But it is suitable for cichlids from lakes Malawi and Tanganyika.

Grain Size

Grain Size (Soil Particles)

The size of soil particles should be determined by the species of fish and plants. Those are planned to be kept in the aquarium. The main condition of the soil is that it must be porous in order to ensure metabolic processes. For example, fine sand quickly cakes and the roots of plants in it will rot, in addition, in such a substrate, water circulation is impeded, due to which it will “turn sour”, bubbles of marsh gases (methane, hydrogen sulfide) will begin to form.
When using a bottom filter, the soil is selected in such a way that its particles do not clog the filter and provide a free flow of water through it.

Soil Types By Particle Size And Application

UP TO 0.5 MM

The fine sand of this fraction is mainly used for decoration. The thick layer quickly cakes and is unsuitable for plant roots. The granular structure of aquarium soil, on the other hand, resists caking and silting and is suitable for plants. Usually, fine-grain soil is used in conjunction with coarse-grain. The small fraction is safe for bottom fish. Not suitable for keeping large fish. While driving, they can lift a suspension of particles that are likely to enter the filtration system.

1–2 MM

Regardless of whether it is ordinary soil or soil, a substrate with similar particle size is suitable for keeping practically all types of medium and small fish. Especially for those who live near the bottom and sift it through the gills, as well as for most plants. Due to the small particle size, it is not recommended to fill in a thick layer of soil. 

In large aquariums, it is advisable to mix with large ones to form the desired substrate height. Or pour a thin layer near the front wall. Likewise, fine grain soil, not suitable for keeping large fish.

3-5 MM

This is suitable for all fish and aquariums of any size, as well as for most large rooting plants. In such soil, silting occurs more slowly, and it is also possible to organize a bottom filter. An exception is a fish that requires a fine substrate.


A substrate layer of such coarse particles. As a rule, is not suitable for plants when used in their pure form. If mixed with fine soil, then rooting becomes possible. It will be appropriate in aquariums with fish that do not care about the presence of soil as such. For example, those who live in the water column and near the surface. Such gravel soil is indispensable in aquariums imitating the bottom of a river with a turbulent current, for example, when keeping char.

Soil Color

Probably the most controversial aspect when choosing soil. The editors of our site are sure that for a freshwater aquarium with tropical fish. It is worth using substrates of natural colors and shades found in nature. The use of exceptionally light or bright-colored soil can affect the color of the fish. It will become dull, faded – this is a process of adaptation to the environment. It is advisable to use colored primers in limited quantities during registration.

Soil Option

Acquisition And Preparation Of Soil

The soil can be purchased at pet stores, via the Internet, or by yourself. But the latter is less preferable since there is a high probability of bringing pathogenic microorganisms and/or hazardous substances and compounds into the aquarium. The risks are especially high if the collection takes place near large settlements.

Purchased soil, with the exception of the soil for the aquarium. It is usually washed in running water to remove dust, small chipped particles that occur during transportation. Some manufacturers supply already treated, practically sterile soils that do not require rinsing. The aquarium soil is prepared according to the manufacturer’s instructions on the packaging.

In this case when the soil material was collected in natural reservoirs or other places, careful processing will be required to remove debris and various contaminants, as well as destroy pathogenic microorganisms. To do this, the soil must be cleaned, constantly shaking and stirring, until the water becomes clear. 

Then the soil is subjected to heat treatment – boiled in water and ignited, for example, in an oven. But this does not give any guarantee that any substances did not remain on the surface of the soil or did not turn into other compounds. Therefore, the collection of a substrate for an aquarium in nature is always fraught with risk.

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