Different types of substrate for a planted aquarium

Pea gravel

The most common form of aquarium gravel is called pea gravel, due to its smooth, rounded appearance. Pea gravel is available in a number of different grades, although only the smaller grades should be used as a main substrate. Although pea gravel is generally inert, it does contain some rock types that may affect the hardness of the water. Aquatic plants will not benefit much from pea gravel, except as a rooting substrate.


Quartz gravel

Quartz is a completely inert substrate and ideal as a main rooting medium and/or top layer for the planted aquarium. Quartz gravel is often sold

Sand as a substrate

Sand Fine-grade sand can cause problems if used as the sole substrate in an aquarium. Over time it will compact, preventing water movement and causing anaerobic conditions, which result in stagnation and the release of toxins. Stirring the sand gently and regularly will prevent this problem, although most plants do not appreciate constant' disturbance. However, due to its small size, sand is very effective at distributing heat in a localized area, such as around a heating cable. If the sand layer is not too deep (about 1.6 in/4 cm), convection currents from a heating cable will ensure a small amount of water movement through the substrate, allowing useful anaerobic conditions to develop without stagnation. When using sand, be sure to choose a completely inert form. Many commercial sands contain traces of lime or calcareous materials, although most of the products sold by aquatic retailers are safe. Silver sand is commonly available and suitable for the aquarium.




Laterite/clay substrates

Clay-based substrates, often called laterite, are usually available as a substrate additive, reflecting the fact that only a small amount is needed. These substrate additives are usually very fine, sometimes even powdery, and reddish colored. They release a number of nutrients, including iron, over a long period. Clay-based substrates are best used as a layer toward the bottom third of the substrate or mixed in with the lower half of the main substrate. This is where the fine roots absorb the nutrients.




Nutrient-rich substrates

Certain planting substrates are specifically designed for aquarium plants. Most of these substrates are laterite-based but contain additional organic and mineral materials that release a number of nutrients over long periods of time. Special planting substrates are available as additives and as main substrates. Use additives in small quantities, either as a thin layer or mixed with the main substrate.

Soil-based substrate

Generally speaking, beginners should avoid using soil in the aquarium, as results can vary wildly. However, more experienced aquarists find that soil can be one of the best long-term planting substrates. It contains large amounts of carbon and iron, both readily used by aquatic plants, as well as a number of other nutrients that are slowly released or retained by the soil. If you do decide to use soil, a 1-1.5 in (2.5-3.75 cm) layer of soil used as a base layer and main substrate, topped with 1 in (2.5 cm) of fine gravel, will suit most aquariums. The safest strategy is to use only sterilized potting mixture - not garden soil - to prevent contamination.
Due to the breakdown of organic matter within the soil, low levels of C02 are constantly released. In many planted aquariums with a soil substrate, additional C02 fertilization is not needed and neither are additional substrates or iron fertilization.

During the first few weeks of soil use, the aquarium may experience a high release of nutrients and organic matter.

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Different layers of substrate in planted aquarium

Several different substrates are available for the aquarium, and making the right choices can be a little tricky. It is possible to have a reasonably good planting substrate using just one medium, although combining a number of substrates will usually produce much better results. When mixing substrates, bear in mind that each one should have a place and a function. Assessing substrates on the basis of their usefulness for a specific purpose will make it easier to choose the right ones.

Base substrate:
A base substrate is necessary only when a heating cable is present. To be effective, the heat from the cable must be well distributed through the surrounding substrate and this is easy to achieve using a very fine substrate with a particle size of about 0.04 in (1 mm). Sand is ideal for this purpose, but use just enough to cover the heating cable.
Main rooting substrate The main body of substrate is used principally as a rooting medium, but also for the uptake of nutrients. This substrate should be compact enough to prevent excess
water movement and oxygenation, but loose enough so that it does not become stagnant and produce toxins. A grade of 0.08-0.12 in (2-3 mm) is suitable and the substrate can be mixed with nutrient-rich additives. More than one main substrate can be used.

Nutrient-rich substrate:
This substrate should provide the plants with a constant and long-lasting supply of a range of nutrients. Depending on the concentration of nutrients present, use either a wafer-thin layer or a layer 0.4-1.6 in (1-4 cm) deep. Nutrient-rich substrates are usually highly compact and soil-like, so "sandwich" them between other substrates to prevent muddying of the water. Some nutrient-rich substrates can be mixed with the main rooting substrate.

Top level substrate:
This will be the most visible substrate and need only be a thin layer placed on top of other substrates. It need not provide any function for the plants and may be used purely for aesthetic purposes.

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Concepts of Substrates in the aquarium

In an average aquarium, the substrate is likely to be a fairly straightforward affair, usually a simple covering of pea gravel. Plants use the substrate not only as a place to root, but also as a source of nutrients and, in some cases, a medium through which to reproduce. The root systems of aquatic plants vary between species, but all are highly evolved to work effectively in a given natural environment. Most of these environments are nothing like those found in an aquarium with a simple pea gravel substrate. Difficulties encountered when keeping aquatic plants can often be attributed to the lack of a good, useful substrate. Clean, inert gravel creates a fairly biologically inactive substrate. Because the water flows easily through such a medium, it removes nutrients, cools the plant roots, and creates an oxygen-rich area, all of which are undesirable and hinder the development of aquatic plant roots.

So which substrates are best? This is not an easy question to answer. Some plants do not need any specialized substrates, while a few need no substrate at all! However, for the most part, a mixture of substrates will create an environment suitable for all the plants in the aquarium. The points to consider are: the size and shape of the particles, the depth of the substrate layer, and its mineral and organic content.

Size and shape

If the particle size of the substrate is wrong, it may cause problems for aquatic plants. A substrate made up of particles that are too large will allow water to pass through easily, removing nutrients. Furthermore, debris will collect in the gaps between the particles, which
may muddy the water. Large-grade substrates also cause problems for the growth of long roots and should be used only as a thin top layer.

If the substrate is too fine it may compact, halting the movement of oxygen and nutrients, and causing damage to the root structure.

A suitable aquarium substrate should have a particle size of about 0.04-0.12 in (1-3 mm) and be rounded in shape; sharp substrate particles can damage roots. The only exception is sand, which can be used as a thin bottom layer to support heating cables, but not required in most of the Indian conditions.

Substrate depth

Substrate depth does vary a little, depending on which species of plant you are keeping. Plants that produce long roots, such as Echinodorus species and some cryptocorynes, will need a substrate deep enough for the roots to penetrate. If the substrate is too shallow, the roots of these plants will become dense and tangled. In this situation, the plant cannot obtain nutrients and the roots will become starved of oxygen.

Generally speaking, foreground plants do not produce long roots, so it is possible to slope the substrate upward toward the back of the aquarium. This also makes the aquarium appear deeper than it is. A good substrate depth is 2.4-4 in (6-10 cm).

Mineral content

Plants require minerals in small amounts, but it is difficult to provide these through the substrate, although some nutrient-rich substrates do contain the essential minerals that aquatic plants require. In general, the quantities of minerals required by plants are usually readily
available in tap water. However, if the source water for your aquarium is relatively soft it may be lacking in these minerals, in which case you can use liquid fertilizers.

More importantly, a substrate should not contain harmful minerals, most notably, compounds with a high calcium content. Limestone and coral-based substrates, often available for marine aquariums, are high in calcium and should never be used in a freshwater planted aquarium. Substrates such as these will increase the alkalinity and pH of the water, making it harder for plants to obtain nutrients and C02.

Organic content

The organic content of a substrate includes organic nutrients, as well as waste matter from the aquarium (mainly from fish). A substrate without any organic matter is simply an "anchor" for the plants and of little other use. You can add organic matter by using a nutrient-rich substrate, which can either be mixed with the main substrate or arranged as a layer between two substrates. Soil and peat have a very high organic content, so use them with care to avoid overloading the aquarium with organic matter.

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Substrate in nature

In the rivers and streams in which many aquatic plants grow, the substrates vary depending on the environmental and geological conditions of the river system and the local area. Aquatic plants are often found in sandy, muddy, or gravel beds. An important point to bear in mind is that in virtually all natural areas the substrate is usually warmer than the surrounding environment. This happens because the heat from the sun is absorbed and retained by the substrate. The difference may be less than one degree but it is enough to create convection currents between the substrate and the water. These currents slowly and continually move water down through the substrate (where it warms up slightly) and back up into the main water body as it cools. As water passes through the substrate it takes nutrients with it, giving the roots access to a continual supply of nutrients.

The dense muddy substrate found in many places provides an ideal anchoring medium that holds plants firmly in position. In natural conditions, the roots may grow far wider and deeper than they possibly could in the aquarium. When keeping some larger plants, such as many of the larger Echinodorus species, take into account the fact that their roots will quickly spread and literally "take over" the aquarium substrate if allowed to do so.

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