Aquarium gravel, or bottom cover as it is sometimes called, is more than just a decorative element used to make the aquarium appealing.

Gravel comes in many sizes and colors.  It can be a fine sand-like material or it can be an assortment of pebbles of varying sizes.  Depending on the type of aquarium being assembled, the gravel chosen for the bottom cover should be selected for its’ role in your aquarium as opposed to how it looks aesthetically.

The fish in your aquarium (if you choose fish as the primary occupant), vary in their perception of color.  Some coral dwelling fish have excellent color differentiation eyesight.   In fact, many coral dwelling fish exceed humans in their abilities to see color in the ultraviolet spectrum.

Other fish (deep sea carnivores) have adapted to low light environments and see only shades of blue.

Probably the most valuable characteristic of gravel is its’ ability to distribute weight across the glass floor of the aquarium.  When creating a decor in the aquarium it is common to see a medley of stacked rocks.  The rocks are organized in such a manner to provide nooks and crannies for fish and other aquatic organisms.  To create pass-through areas it is often necessary to stack a series of rocks one upon another.

If there were no gravel substrate on the aquarium floor, rocks would balance on a few points causing all their stacked weight to press down at those few points.  With all the weight resting on just a few points the liklihood of a floor crack would increase significantly.

Adding gravel to the aquarium floor and placing aquarium rocks on the gravel, as opposed to the glass, creates a weight distribution area.  With the rock weight distributed across a much larger area the pressure is removed from just a few points and spread out across thousands of points.

In addition to the weight distribution advantages of gravel, Gravel also provides mechanical stability to the rocks stacked in the aquarium.  With a more stable base for the rocks the potential of rocks to tumble and land on the aquarium floor diminished significantly.

Many aquariums enjoy a variety of flora to enhance the visual appeal of the aquatic environment.  Aquarium flora also enhance the water chemistry creating a balance in managing CO2 and O2 water gases.

In order for flora to accomplish their task of assisting in water chemistry management, they need to be well rooted in the aquarium.  If they are not well rooted the plants will rise to the surface and block light from reaching other plants.

Gravel provides the medium for holding down the roots of the plants so that they can flourish without affecting other plants negatively.  Well rooted plants use the nutrients in the gravel to provide the plant with sufficient raw elements from which it can thrive.

Not only does gravel support a varied nutrient mix to the roots of aquarium flora, gravel also provides a critical surface biome for bacteria.

As the aquarium moves from its’ startup phase to a more mature biome, the gravel in the aquarium takes on a new role.  The natural life cycles of aquarium occupants result in waste products that are suspended in the water for a time and, to some extent, filtered out by the aquarium filters.  The remaining waste products find their way to the floor of the aquarium and settle in and among the granules of gravel.

It is here, on the gravel floor, where gravel provides a large surface area that is beneficial for bacteria to grow.  The bacteria aids in the decomposition of occupant waste and breaks down harmful ammonia into less toxic substances like nitrates and nitrites.  The nitrates are beneficial to the aquarium flora helping them to flourish.

The water filtration equipment added to the tank is responsible for removing large amounts of physical waste products and non-consumed food.  the balance of suspended organic particulates precipitate through the water ending up lodged in the rough terrain of the gravel floor.

The lodging of this material in the uneven surface of the gravel further assists in the process of keeping the aquarium water clear.  After bacteria has broken down the organic material only inert material is left and it gathers on the surface of the gravel.

This material will continue to accumulate until an aquarium vacuum is used to process the floor gravel and remove the inert material.  Fortunately, bacteria are very small and an aquarium vacuum will never be able to remove all the bacteria.  Thus, the aquarium biome is protected and will once again flourish once additional material settles on the gravel floor.

Just as there is a wide variety of gravel types, there are a wide variety of aquarium occupants that use gravel for differing purposes.

The selection of gravel for the aquarium should take into consideration the aquarium occupants.  Many fish species sift through gravel looking for food or make use of gravel for nests.

Certain bottom-dwelling fish and invertebrates also rely on gravel for their natural behavior and habitat.  Exercise caution when selecting gravel to make certain the gravel selected is compatible with the species of occupants expected on your aquarium.

Generally speaking, the larger the fish the larger the gravel.

Some aquarists build out a biome for crustaceans or other aquatic species that are not fish.  Often these species are large waste producers.

Turtles, particularly carnivorous snapping turtles, produce large amounts of waste products.  This can present a problem for aquarists with smaller sized aquariums.  The waste material can quickly overcome the ability of the water to buffer against ammonia, and quickly overwhelm the aquarium particulate filtration system.

In these situations, the floor gravel will become over saturated with organic material and require a vacuum to clean the gravel.  Plan ahead for these types of occupants and use larger sized gravel that can be easily cleaned with a vacuum attachment.  Small sized gravel( like sand) is often removed during a vacuum session.  Whereas, larger gravel will remain in place and only the organic materiel will be removed.

Who knew gravel was so important?  Selecting the correct gravel means the aquarist needs to make the decision earlier as to who the occupants will be in the aquarium.

An aquarium construction note:  Be sure to wash your gravel before it is introduced to the aquarium.  Keep in mind that gravel is crushed rock.  Many types of rock will change the pH of your aquarium water.  When adding gravel to an existing already occupied aquarium, do so in small amounts – checking the pH an hour or so after adding the gravel.