Choosing the right substrate for your aquarium is much more than just a question of aesthetics. It is a decision that will directly affect the health of your plants, fish, and the entire ecosystem as a whole. The right substrate will become the foundation for life in your underwater world.
Modern aquarium soil performs several key functions. It serves as an anchor for plant roots, a habitat for beneficial bacteria, and a natural filter. In addition, it affects water parameters such as hardness and acidity, which is especially important for sensitive species.
Understanding these basics will help you make an informed choice. Below, we will look at the main types of substrates, their pros and cons, and what you should pay attention to in order to create a beautiful and, most importantly, sustainable aquarium.
Impact on the hydrochemical composition of water
Just like natural decorative elements, some types of natural substrate can affect the hydrochemical composition of the water. For example, dolomite or marble chips increase the dGH index, while anthracite-based substrate acidifies the water. Artificial substrates, as well as sand, crushed and polished granite, basalt, quartz, and others, have neutral properties. Aquarium substrate usually acidifies and softens the water, which is an ideal environment for most plants to grow.
For example, you should not use a substrate made of marble chips (increases dGH) when keeping Betta fish, gouramis, most tetras, danios, and others. However, it is suitable for cichlids from Lake Malawi and Lake Tanganyika.
Grain size (substrate particles)
The particle size of the soil should be determined by the types of fish and plants that are planned to be kept in the aquarium. The main requirement for the soil is that it must be porous to ensure metabolic processes. For example, fine sand quickly clumps together and plant roots will rot in it. In addition, water circulation is difficult in such a substrate, causing it to “sour” and form bubbles of marsh gases (methane, hydrogen sulfide).
When using a bottom filter, the substrate is selected so that its particles do not clog the filter and ensure free water flow through it.
Types of soil by particle size and area of application
Up to 0.5 mm — fine sand of this fraction is mainly used for decoration. A thick layer quickly clumps together and is unsuitable for plant rooting. The granular structure of aquarium soil, on the other hand, resists clumping and silting and is suitable for plants. Usually, fine-grained soil is used in combination with coarse-grained soil. The fine fraction is safe for bottom-dwelling fish. Not suitable for keeping large fish. When moving, they can stir up particles that are likely to enter the filtration system.
1–2 mm — regardless of whether it is regular soil or substrate, a substrate with this particle size is suitable for keeping almost all species of medium and small fish, especially those that live near the bottom and sift through it with their gills, as well as for most plants. Due to the small particle size, it is not recommended to pour a thick layer of soil. In large aquariums, it is advisable to mix it with coarse soil to form the desired substrate height, or to pour a thin layer near the front wall. Similarly, fine-grained soil is not suitable for keeping large fish.
3–5 mm — the “golden mean,” 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. The exception is fish that need a fine substrate.
More than 5 mm — a layer of substrate with such large particles is usually not suitable for plants when used in its pure form. If mixed with fine soil, rooting will be possible. It will be appropriate in aquariums with fish that do not need soil as such, for example, those that live in the water column and near the surface. Such gravel soil is indispensable in aquariums that imitate the bottom of a river with a strong current, for example, when keeping loaches.
The right substrate for an aquarium is not just a decoration, but the basis of a healthy environment for fish and plants. It affects water purity, plant root development, and the comfort of bottom dwellers. When choosing, pay attention to the fraction — too fine a substrate can become clogged with food debris, and too coarse a substrate can injure fish. It is better to choose rounded gravel or medium-grain sand. If there are plants growing in the aquarium, it is worth adding a nutrient layer or choosing a substrate with minerals. And remember: before laying the substrate, it must be thoroughly washed so that the water does not become cloudy.
Substrate color
This is probably the most controversial aspect of choosing a substrate. Our editorial team believes that for a freshwater aquarium with tropical fish, it is best to use substrates in natural colors and shades found in nature. The use of exclusively light or brightly colored substrate can affect the color of the fish, making it dull and faded — this is a process of adaptation to the environment. It is advisable to use colored substrate in limited quantities when decorating.
It is not uncommon to find substrate on sale that is dangerous for aquarium inhabitants — often it is brightly colored, handmade gravel covered with ordinary waterproof paint or enamel used in construction for painting walls. In water, such soil will release substances that are toxic to fish and plants. Clear signs of counterfeiting are chipped, flaking paint, a pungent odor that can be smelled even through the package, and the absence of any manufacturer's markings.
Here is everything you need to know to choose the right substrate for your aquarium. As you can see, it's not just a question of beauty. All life in your little underwater world depends on it.
The main thing is to remember that there is no single correct option. It all depends on your plans. If you want a lush garden with plants, choose a nutritious substrate. If you dream of a school of bright fish, opt for neutral soil that will simply decorate the aquarium and do no harm.
Don't go for crumbs that are too small or colored. Give preference to proven, natural materials. And, of course, always consider the needs of your future pets — this will be their home.
Take the time to choose now, and your aquarium will give you years of enjoyment without any hassle. Good luck!
