Substrate for a planted aquarium.
The main consideration when choosing a substrate is what kind of aquarium you are going to use it for. For a fish aquarium with plastic or undemanding plants like Anubias, the choice of substrate is not very important, as it mainly serves decorative purposes. If you are not interested in growing plants (e.g., you prefer plastic plants) or if undemanding plants like Elodea grow in the aquarium, you can use fine gravel as a substrate. You can also use decorative substrate sold in a pet/aquarium store.
The substrate has three main functions. The first is to support the life of aquarium plants and supply them with nutrients. The second is to allow microorganisms to multiply and stabilize the aquarium environment. The third is to give the aquarium a natural look. The aquarium should be set up so that all aquarium plants with their various needs can grow healthy.
The substrate is an imitation of a real river or lake bed. Many people mistakenly believe that it plays only a decorative role in the aquarium. Its main purpose is to provide a natural bottom for the world of fish and plants. Substrate is an important element of the aquarium’s biological system, and its composition is crucial for maintaining biological balance in an artificial body of water. It is in the substrate that the main biochemical processes determining the biological balance of the ecosystem take place. For an aquarium containing plants, the substrate is of primary importance. Plant roots grow in it, and plants receive nutrients from it. The presence of nutrients in the substrate is especially important for plants with a developed root system, such as Cryptocoryne.
This is not only soil for aquatic plants, but also a substrate for microorganisms responsible for processing fish waste products. Even a thin centimeter layer of substrate at the bottom serves as a primitive yet effective biofilter. Bacteria, single-celled organisms, and algae live in the substrate and take part in the processes occurring in the aquarium. On the other hand, the substrate can act as a buffer to change the chemical parameters of the water — for example, in an aquarium with African Cichlidae, a substrate containing a lot of limestone is usually used to maintain high water hardness.
Microbial activity is especially important because organic substances, such as fish waste and food scraps that enter the substrate, are processed by microorganisms living in the substrate. In addition, aquarium plant roots and microorganisms in the substrate exist in a certain symbiosis. Aquarium plants can grow well only when microorganisms help them absorb nutrients through their roots.
When aquarium plants grow densely, consuming nutrients derived from organics, the absorption of nutrients from the leaf surface and the release of oxygen through photosynthesis are also activated, and the aquarium environment stabilizes. Beneficial microorganisms living in the substrate include bacteria, fungi, and protozoa. The supply of organic matter on which they feed and oxygen are essential for enhancing their growth and activity.
Usually, a substrate is placed at the bottom of the aquarium, which is primarily needed by plants whose roots anchor in it and receive nutrients from it. Most cultivated aquarium species are bog/marsh plants that receive most of their nutrients through a branching root system from the soil and only a small amount through the plant surface. In aquatic plants, roots are so small that their main task is anchoring in the substrate. They absorb nutrients to a very small extent.
Such plants feed almost exclusively on ions dissolved in water, which are much fewer in water than in soil. When optimal vegetation is desired in the aquarium, it is necessary to make sure when setting up the aquarium to choose a substrate material that contains a sufficient amount of nutrients.
In nature, plants (including aquatic ones) grow on four main types of substrates (according to prevailing substances):
•— Calcium-containing rocks (marble, dolomite, chalk, gypsum, coquina, etc.);
•— Silicate rocks (silicate sand, granite, porphyry, sandstone, serpentine, etc.);
•— Laterites (basically aluminosilicates);
•— Organic substrates (e.g., peat).
Plants growing on calcium rocks must have special mechanisms allowing them to consume nutrients, because calcium not only blocks the absorption of other nutritional elements, but also interferes with the processing of plant residues into humus by microorganisms. For these reasons, the use of calcium-containing rocks in planted aquariums is highly undesirable.
Laterites are mainly characteristic of the tropics and humid subtropics, where it is hot and there is enough moisture for the continuous destruction of organic matter. However, the presence of aluminum leads to the rapid binding of many trace elements by complex salts. As a result, a sort of slurry of poorly soluble inorganic substances is formed, resembling a very fine and very viscous clay. Iron in such soils, for example, precipitates as a hydroxide. One must also know how to grow in such acidic ferruginous soils. The lion’s share of tropical aquatic plants inhabits precisely such soils. Typical in this sense are Cryptocoryne from Sri Lanka, most species from Southeast Asia, the Amazon basin, the Orinoco, Zaire, and the Congo.
Granulated red Sri Lankan soil sometimes appears for sale, which is used as a bottom layer under fine-grained substrates when setting up a planted tank. The mechanism of its action (and various clays) is based on the fact that, entering completely different environmental conditions, it begins to release the microelements contained in it, and at the same time rapidly lowers the redox potential of the substrate (since it introduces a large amount of unoxidized or incompletely oxidized substances, causing a sharp increase in the consumption of dissolved oxygen). The use of peat in aquariums is based on approximately the same principles, with the only difference that in most cases serious help from saprophytic microorganisms is also required here.
Silicate rocks are mostly neutral, both regarding the absorption of nutrients by plants living on them and regarding the processing of plant residues by microorganisms. Among aquatic plants, running-water plants of temperate latitudes have adapted well to living on such substrates. These are the most acceptable types of substrates for aquariums.
Thus, only silicate rocks are the main components of the substrate for planted tanks. Other types of substrates should not be used as the main substrate at all or can serve only as auxiliary additives.
Which types of substrates are suitable for plant roots. Chemical composition of the substrate.
Glow-in-the-dark aquarium substrate. 
Last changes and additions were made on August 12, 2012.
