Type of substrate
Main rooting substrate
Small-grade pea gravel can be used as a main substrate.
Ideal top-level substrate.
Small grades can be used with a heating cable.
Ideal as a main substrate.
Looks good as a top layer, but due to the small grade, mulm will collect more readily. Not normally a major problem.
Ideal for use with a heating cable.
Not suitable due to compaction.
Some nutrient-rich substrates are designed to be used in large quantities as a main substrate. If the grade size is greater than 0.16 in (4 mm), mix it with a smaller lime-free substrate.
Suitable if covered by a 1 in (2.5 cm) layer of gravel.
High, may be lacking hardwater nutrients.
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.
Types of substrate
Here we look at commonly available aquarium substrates and their suitability.
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
Silver sand is made up of very fine grains. Its compact nature makes it an ideal medium for heat transfer and a good supportive medium. When using a heating cable, sand is the best medium to cover the base of the aquarium.
Laterite-based substrates are ideal as a long-term source of nutrients. Laterite can be mixed in with the main substrate or used toward the lower half of the substrate, where plant roots are most effective at obtaining nutrients.
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