Aquarium substrates provide many purposes. Not only do they look visually appealing, they also provide a medium for aquatic plant roots to establish, help regulate water temperature, provide a place for growth for beneficial bacteria, give bottom feeders a better surface to move around on and also a stable surface for anchoring aquatic decorations.


Image result for aquarium gravel

Aquarium gravel is the most popular aquarium substrate because of its simplicity. Aquarium gravel is the ideal medium for most tanks, any type of fish and aquatic creatures.

Aquarium gravel is not like the gravel on the street. It has much smoother edges, it will sit more regularly, the gaps will be regular, it will look more aesthetic, it will not damage your tank or your fish, also, aquatic plant roots can wrap itself around the aquarium gravel without being cut once the plant is moved (the roots will not be ripped).


Image result for aquarium sand

Aquarium sand is another commonly used substrate. Sand has a much smaller grain size than aquarium gravel. Often, this is close to what fish experience in the wild, it is ideal for fish that like to bury themselves, providing an added sense of privacy and security which will help to decrease stress and increase health in many species of fish.

However, due to the tiny size of the sand, they can often be easy to move around and cause damage to your tank filters. Usually, you don’t need to worry about the sand choking the fish, fish have gills designed to pass out small particles like this.


Image result for coral sand

Coral gravel is the general name given to small, hard particles containing calcium carbonate. It may be easier to call it “coral gravel” because the particles are generally gravel sized. This substrate consists of calcium carbonate and dissolves in water with time.

In additional to just tank decoration, coral sand fights acid buildup and raises the pH and hardness of the tank. This makes coral sand an ideal substrate if you have fish that prefer an aquarium with a higher pH level.


Image result for marble chippings

Marble chips are similar to coral sand except they are heavier and less porous.

Marble chippings are also cheaper than many other substrates, however they usually come with unrefined sharp edges which may pose a problem.

If you do not wish to change the pH of your aquarium than marble chippings are suitable because they are chemially unreactive. However,

One of the main functions of the substrate is to provide a place for the growth of beneficial bacteria. Substrates, especially pebbles and gravel with relatively large grain sizes have a sizable gap allows the water to remain stagnant, also providing a sizable gap allowing bacteria to grow and also prevent fish from swimming around and disrupting bacterial growth. The bacteria can act as a biological filtration system. Because the numerous particles of the substrate forms a collective high surface area, substrates can easily be employed in biological filtration. Common filtration methods involving the substrate include the undergravel filter and deep sand bed.

The substrate color has a direct effect on fish. A dark color substrate are considered to be better for fish. First of all in nature substrates are more likely to be dark colored than light, think of the dark colored rocks and mud in streams. When a dark color substrate is used not only do fish appear to be more brightly colored but they also behave more timidly due to less agitation from bright lights, dark colored substrates reflect less light which makes it easier for fish to get rest at  night.

Substrates can double as a method to alter the chemistry, pH and nutritional composition of the aquarium. Crushed coral and sand both contain CaCo3 (calcium carbonate) which will raise the carbonate hardness and buffer the water’s pH. Peat moss may also be used in some aquariums to simulate the soft water habitats (low pH, high acidity, alkali, highly basic water is called hard water in contrast).

If you wish to have aquatic plants in your aquarium the substrate must be loose enough so that the aquatic plant roots can penetrate in. The substrate should be free of reactive chemicals and have no sharp edges to prevent roots from being cut when plants move. Finer substrates such as 1-2mm gravel is the preferred medium to be used by many because large, coraser substrates allow debris to fall at the gaps between grains. This makes it difficult to clean and is also visually unappealing in an aquarium. Substrates used for aquatic plants should be at least 2 inches (5cm deep). Most aquatic plants have roots that can extract nutrients from the substrate too. A lower rich layer of substrate can be included such as potting soil, peat, vermiculite and special clays (make sure they are treated for aquarium use unless you want your water to be completely brown!) can be used to provide essential nutrients such as iron for the plant roots.

Large grained substrates which provide plenty of space between particles, such as marbles, can be used in aquariums to house egg-laying fish species, once the eggs fall in the spaces between these marbles the parent fish cannot swim inside and eat them.

CEC – cation exchange capacity.

Cations such as hydroxide and hydrogen ions affect the pH level of the water. This is an important factor to consider when keeping aquatic plants. The cation exchange capacity is the ability to absorb positively charged nutrient ions (a high CEC is good), meaning the substrate will retain nutrients and make them available for plant roots. The CEC however, doesn’t indicate the actual amount of nutrients the substrate contains, it only indicates how freely the nutrients will be released by the substrate.

Substrates which contain high levels of CEC (cation exchange capacity) include the folliwng:

  • Crushed limestone
  • crushed marble
  • crushed skeletons (base constituents of marble)
  • coral sand
  • … and anything else containing calcium carbonate

Substrates high in calcium carbonate are used in hard water aquariums to increase the pH and cause a more alkali environment.

Conversely, peat moss is the main substrate used to lower water pH. This simulates software environments, such as the software aquatic ecosystem in the Amazon river.

Not only is peat beneficial for lowering water pH, providing a soft and comfortable environment for demersal bottom dwelling species, it also acts as an effective ion exchanger, containing substances highly useful for the health of plants and reproductive health of your fish, peat moss can also prevent algae growth and kill harmful bacteria. Peat moss does come with its challenges though, one of these disadvantages is that the water will be stained brown/yellow due to dyes naturally present. Although this can be visually unappealing for some, this discoloration is generally harmless.


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