Aquascaping

While some aquarists maintain aquaria with minimal or no decoration, these are often breeding tanks or tanks for growing out fry. Most fish, however, do not show their best colors and behavior when kept in bare tanks, where they feel exposed.

Live vs. Artificial Plants

Plants serve two main functions in the aquarium: aesthetics for the aquarist and habitat for the fish. If you are happy with plastic plants, your fish will be too.
Live plants will remove some wastes from the water, but dead leaves add to the bioload. Artificial plants don’t reproduce, but they also don’t grow and change your aquascape over time like live plants will.
Live plants will be preferred by your fish if they are herbivorous—fish that like to eat plants will find the artificial ones a very poor substitute!

Coral

Live coral and other invertebrates are the basis of a reef aquarium, and keeping such creatures alive and healthy can be an extremely rewarding experience.
There are also many artificial corals that are extremely lifelike, enabling you to decorate a marine aquarium without the high-tech equipment necessary to keep reef animals alive. These artificial corals can be safely used in freshwater tanks as well, if you are so inclined.

Other Decorative Items

A variety of natural objects and artificial ornaments can bring beauty to your aquarium and habitat to your fish. Natural or fake, fish take security in and around these items.

Rocks: Many fish enjoy hiding in caves and crevices in rock structures. Non-soluble rocks do not alter the water chemistry and include slate, shale, quartz, and others. Soluble rocks like coral rock, limestone, and lava rock slowly dissolve in the water, raising pH and hardness. These are great for marine setups or high-pH freshwater systems.
Driftwood: Like some rocks, driftwood will leach substances into the water, but in this case they soften the water and lower the pH. A few species of catfish require wood in their diet and will graze on driftwood.
Artificial Ornaments: Both rocks and driftwood are available in plastic imitations, but there are thousands of more fanciful decorations available as well, many of which include holes and caverns in which fish can hide. Everything from fairyland castles to sunken ships to human skulls are available for those who like a less natural-looking, more personalized aquascape.

Gravel

Only a few types of fish require a substrate, such as species that bury themselves in the sand. Most people, however, prefer the look of sand or gravel. While many hobbyists insist on natural gravel, there are gravels available in a rainbow of colors, including some neon hues. Your fish will not care which you choose; there are, however, several factors you should keep in mind when choosing your aquarium’s substrate.

There are soluble and insoluble sands and gravels. Crushed coral and crushed limestone will dissolve, raising the hardness and pH, as well as increasing the buffering capacity of the water. These are used in marine setups and with fishes like African Rift Lake cichlids. Insoluble quartz or granite are inert and can be used in any system.
Sand is preferred by a few species of sandsifting fishes, and some aquatic gardeners like sand for their planted tanks. But in general, a medium-grain gravel is best for your aquarium. Fine sands can develop anaerobic (low-oxygen) zones that can be dangerous, and coarse gravel will trap uneaten food and other debris in the large spaces; small fish can even become entrapped.
Many aquarium gravels are now sealed with epoxy. This waterproof coating eliminates the dust normally associated with gravels, and it ensures that the gravel is inert and will not leach chemicals into the water. Such substrates can be used in any type of setup.

How to Prevent Anaerobic Bacteria

I have a 55-gallon African cichlid tank (with some other non-cichlid tankmates, including a catfish) with a pH of 7.6 to 7.8, mildly hard water, and sand substrate. The cichlids don’t bother any of the other fish or plants, but they also don’t dig in the sand like they used to in their previous, smaller tank. I am worried about the formation of anaerobic bacteria. What can I do to prevent this? I was told to stir the sand when I do my water changes, but that would involve removing lots of rocks and plants. Is there a way to prevent this without completely tearing the tank apart every time? Darrel Todd (via email)

Your cichlids may resume their excavations once they get settled in and establish territories. Several species of cichlids sift sand, and they will keep a sandbed aerated. Most cichlids, however, simply dig pits and may ignore large areas of the sandbed entirely.

For the time being, simply stir the sand that you can reach without dismantling the tank. There shouldn’t be a problem with anaerobic bacteria if you perform that simple task regularly, and your catfish should keep the gravel disturbed to some degree.