If you are installing an aquarium in your home or office, there are a number of decisions you need to make regarding size, equipment, and the kind of ecosystem you wish to create. One important decision is the kind of substrate you will use -- the material on the bottom of the tank, in which you will plant aquatic greenery, coral, and other aquatic life. Since the substrate is an important part of your overall ecosystem, you need to choose the appropriate material.

CaribSea Dry Marine Aquarium Substrates

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WorldWide Bio-Activ Live Aragonites Aquarium Substrates

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Natural Pebbles Premium Fresh Water Substrates - 50 lbs

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WorldWide Bio-Activ Live Aragonites Aquarium Substrates

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WorldWide Bio-Activ Live Aragonites Aquarium Substrates

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WorldWide Bio-Activ Live Aragonites Aquarium Substrates

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CARIBBEAN CRUSHED CORAL 20LB, MARINE SUBSTRATES, CARIB SEA, AQUARIUM

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CARIBBEAN CRUSHED CORAL 40LB, MARINE SUBSTRATES, CARIB SEA, AQUARIUM

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A primary function of substrate is as an environment for beneficial bacteria. These bacteria can perform many functions, such as converting fish waste into natural food for aquatic plants. There are hundreds of aquarium substrate products on the market, and many are enhanced with bacteria, minerals, nutrients, and other substances that will facilitate the smooth functioning of your aquarium ecosystem; just make sure that the substrate you select is appropriate for the environment you wish to create.

Primarily, though, a hobbyist will still select a substrate based on aesthetics. Many enthusiasts consider darker-colored substrates to be better for fish. Fish colors display more brilliantly with darker substrates, for instance, and fish are thought to behave less timidly.

For freshwater aquariums, the most common choice for substrate is gravel. The gravel should not be sharp; it can be as coarse as pea-sized in diameter, or as fine as 1-2 millimeters. If your fish population will include bottom feeders, finer gravel is a better choice. Gravel is available in several colors, and can be sealed to ensure that it doesn’t affect water chemistry; gravel that is sold specifically for aquariums is chemically inert. The composition of aquarium gravel is usually quartz and other lime-free minerals.

Another simple choice for fresh water is sand. Sand is very fine and will compact itself over time; it is clean, and available in several varieties, from play sand (which has been sterilized for use by children) to black Tahitian Moon sand. Fish also seem to prefer sand. There are some disadvantages -- because it is compact, debris will rest on top of sand rather than settle into it, necessitating more frequent cleaning. (And, because most sand is light colored, debris will be plainly visible.) And sand can clog your filter. You cannot use an undergravel filter with a sand substrate. Also, if your substrate is purely sand, live plants may have difficulty establishing their roots through this compacted material.

Do not harvest sea sand for use in your aquarium; sea sand contains too many impurities, the effects of which will be magnified in the closed aquarium environment. Choose sandblasting sand (somewhat coarse, mostly composed of quartz), play sand, or some other sand that has been cleaned of impurities.

If you plan to have a number of plants in your aquarium, remember that your plants will obtain most of their nutrients through their root systems, which will be implanted in the substrate. Your substrate should probably consist of two layers: the bottom layer should be nutrient rich, or have the capability to store nutrients, and the top layer should prevent washout of nutrients as well as provide a firm anchor for the plants. In such an arrangement, the lower level should be as high as the plant roots (1-2 inches), and the top layer about 2 inches in height.

In such a dual-layer substrate, the top layer could be gravel, or perhaps sand, though make sure that your plants’ root systems do not have to grow through any of the sandy top layer. As for the bottom layer, vermiculate makes an ideal choice. Vermiculate is a mixture of aluminum, iron, and magnesium; it is generally heated during processing, rendering the mixture sterile, pH-neutral, and with a high surface area. Vermiculate has a high cation exchange rate: this is the process through which plants absorb nutrients from soil. Vermiculate also releases potassium and magnesium over a long period of time, again benefiting your plant life.

Because vermiculate tends to compact, it is best mixed with another substrate material, such as laterite, to maintain a porous structure. Laterite is porous, weathered clay burned by the sun; it contains high concentrations of iron oxide and tends to hold nutrients in storage until plant root systems absorb the nutrients.

Saltwater aquariums, particularly reef aquariums, have different requirements. A fine-grained sand can be used, although sand is not a hospitable environment for bacteria and other microscopic organisms that can benefit your saltwater ecosystem. A better choice might be crushed coral; as calcium carbonate is slowly released from this substrate material, it can promote new growth in any coral formations you have in your tank, and it also helps maintain the high pH levels needed by saltwater fish. Crushed coral should be thoroughly rinsed before laying it in your tank; excessive coral dust can cause your tank water to cloud over.

Another substrate for salt water is aragonite gravel; aragonite is filled with beneficial bacteria and other organisms, and thus is considered a “live” substrate. As with coral, aragonite has a high calcium carbonate content, helping sustain your coral formations and maintaining a proper pH balance in your tank.

There are many choices for an aquarium substrate; however, the kind of aquarium environment you wish to create will go a long way toward determining the most appropriate substrate choice.