Aquarium Substrate

Appearance is often the biggest factor for people choosing an aquarium substrate. The functional aspects of the substrate are often overlooked in favour of aesthetic choices. Considering both look and function can result in a healthier fish tank while still achieving visual harmony.

There are three main substrate attributes you should consider in relation to the fish you choose to keep; colour, particle size and reactivity with the water.

Bare Bottomed Aquarium

The simplest solution when selecting an aquarium substrate is to to leave it out altogether.

Bare bottomed aquariums are cheaper to setup, easier to clean and offer fish a little more space to swim. Such fish tanks are often favoured by practical fish breeders who want to maximise production efficiency.

For a display aquarium the main detraction from such a substrate choice is the appearance. Fish waste and food scraps stand out on the shiny aquarium floor where gravel would generally mask it's presence through camouflage.

Aquarium Gravel

Whether it is gaudy painted pebbles or more tasteful river stones, gravel is the most popular aquarium substrate.

Gravel sold in aquarium shops will usually be chosen for it's smooth edges and inert chemical nature. Such gravels will not injure startled fish or dissolve into the aquarium water.

The gravel size is also important. 3 to 4mm is an excellent size to allow adequate water flow through the aquarium substrate. In doing so the water can be cleaned through biological filtration as beneficial bacteria feed on dissolved fish wastes. Gravel larger than 4mm will allow sufficient water flow but cannot provide the surface area offered by smaller grades.

When choosing a gravel colour keep in mind that it will hide sunken debris more successfully when it contains a number of different shades. All white gravel may seem a decorative fish tank substrate but it will place emphasis on any accumulated dirt and detritus.

Aquarium Sand

Sand as an aquarium substrate is useful with bottom feeding fish with delicate barbells. By using sand instead of gravel these delicate appendages will not be damaged as the fish scavenges for food.

The biggest problem with sand as an aquarium substrate is it's fine diameter. When placed thickly on the aquarium floor, areas can form where there is no water circulation. In these anaerobic conditions no biological filtration can be achieved. If sand is the aquarium substrate you choose, be sure to use it in a thinner layer to reduce this problem.

The fine particle size is also problematic when cleaning the substrate. If water is siphoned from the bottom using a hose or gravel cleaner the sand will be lost with the removed water.

Coral Sand

Coral sand is better described as a coral gravel. Coral is made of calcium carbonate which steadily dissolves in the aquarium water. As the coral dissolves it counteracts the acidifying processes associated with decay of food and the release of fish waste. This pH buffering quality makes coral sand a very practical aquarium substrate for fish that enjoy hard water and a higher pH.

This product is more expensive than gravel and will not hide dirt due to its light colour. The very light colour can also be distressing to fish, especially when illuminated with strong lighting. Without dark surroundings the aquarium inhabitants can feel unsettled. They may become stressed and lose their natural colour in an attempt to blend with the bright surroundings.

Marble Chip

Marble chip is another calcium carbonate based fish tank substrate. It does not have the same structure as the porous coral sand. This makes marble chip heavier and gives it less surface area than coral sand. The reduced surface are gives it slower buffering qualities and fewer sites for biological filtration to be performed.

On the positive side marble chip is a less expensive aquarium substrate than coral sand and is available in shades other than white.

Aquarium Substrate Final Note

All substrate materials should be thoroughly washed before use. Fine particles need to be rinsed away or they will become suspended in the water causing cloudiness.

Many gravels and sands can be purchased from garden centers at a more reasonable price than pet shops.

Further considerations should be made when choosing a substrate for aquarium plants. For best results you may need to add substances such as laterite to allow correct uptake of nutrients.

When filling the aquarium with water there are times when you will not want to disturb the aquarium substrate. This can be achieved by placing a plate on the gravel or sand before pouring in the water.

Aquarium Substrate in Action

This aquarium gravel allows aquatic plants to be grown by offering a stable substrate. Note how it is light enough to give the aquarium a sense of open space, but dark enough to hide waste.

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