When faced with beautiful aquariums filled with fish, it can be tempting to choose specimens based solely on their appearance. However, fish do not all share the same dietary and environmental needs. Some species are herbivores, others omnivores or carnivores. Mixing species is often discouraged to prevent nutritional deficiencies and predation. Certain fish also have more aggressive temperaments and must be kept in carefully selected community settings.

Water parameters vary depending on the species as well. For an Amazonian-style aquarium, the water should be soft and slightly acidic, whereas African cichlids require hard water (high in minerals) that is slightly alkaline.

Once you’ve chosen your fish, it’s time to set up your aquarium. First, select the tank size. The larger the tank, the more fish it can accommodate—and the easier it is to maintain a stable environment. While starting with a small aquarium may seem appealing, it is actually more difficult to maintain and keep water conditions optimal. And if you catch the aquarium hobby bug, you’ll likely want to upgrade to a larger tank quickly!

You’ll also need to decide where it will be placed. A large aquarium is very heavy—remember that 1 liter of water weighs 1 kilogram (2.2 pounds), not including the weight of the tank itself. It cannot be placed on a weak or unstable piece of furniture. Additionally, avoid direct sunlight hitting the tank, as this will promote excessive algae growth.

Substrate

The substrate is the material covering the bottom of the aquarium, typically sand or gravel. It comes in various colors and sizes, allowing you to customize both the habitat and the appearance of your tank. Larger gravel is generally easier to clean.

Some fish have specific preferences related to breeding or natural behaviors, such as digging in sand or hiding among rocks. Certain substrates can also help maintain specific water parameters. For example, coral sand is recommended for hard, alkaline water.

Décor

Natural or artificial plants? Knowing your fish species will help guide your choice. Some herbivorous fish may eat live plants, while others may struggle to thrive in hard, alkaline water conditions.

If you choose live plants, you’ll need appropriate lighting—often including a UV or full-spectrum light—to support plant growth, as well as a suitable substrate. When designing your aquarium, it’s also essential to provide multiple hiding places to help your fish feel secure.

A fish’s health depends heavily on water quality—especially the nitrogen cycle. Fish eat, breathe, and eliminate waste in the same water. Feces and uneaten food produce ammonia, which is highly toxic. Beneficial bacteria convert ammonia from organic waste into nitrites, which are still toxic, and then into nitrates, which are far less harmful.

A rapid rise in ammonia or nitrite levels can lead to the death of all your fish within hours.

Once the aquarium filter is started, it typically takes about one month to fully establish the nitrogen cycle. The presence of live plants, a small initial number of fish, and certain products available at pet stores can help speed up the process. It is strongly discouraged to add a large number of fish too quickly, as this can cause a sudden spike in nitrites and result in the loss of your new companions.

Investing in a high-quality filtration system may be costly, but it will save you significant time, effort, and potential problems in the long run. Keep in mind that filter components must be cleaned and replaced as needed. Regular water testing is essential to monitor nitrite, nitrate, and pH levels—several reliable test kits are available at pet stores.

Depending on your municipality, tap water parameters can vary greatly. It is important to test your tap water to determine whether it is suitable for your fish. Products specifically formulated for aquariums can help adjust pH, reduce nitrites and nitrates, remove chlorine, modify water hardness, and support the beneficial bacteria required for the nitrogen cycle.

To refresh the water and reduce organic waste and nitrate buildup, partial water changes are necessary. Typically, 10–15% of the aquarium’s volume is replaced every two weeks. More frequent changes may be required in cases of overstocking or if nitrate levels are elevated. Using a siphon—essentially a type of vacuum—you can remove debris and waste from the substrate while simultaneously draining water. However, it is generally not recommended to remove and wash the substrate entirely, as beneficial bacteria that help convert ammonia into nitrites and maintain a healthy cycle reside in the gravel or sand.

An air pump or aeration system can also increase the amount of oxygen available to your fish. A heater will help maintain a consistent and appropriate water temperature.

The closer your aquarium’s water parameters are to your fish’s natural habitat, the healthier they will be—allowing them to grow properly and display vibrant colors.

Unfortunately, very few veterinarians treat fish. However, most health issues are secondary to poor water quality. If you are concerned about your fish’s health, begin by testing your aquarium water. Based on the results, make the necessary adjustments to nitrite, nitrate, pH, and hardness levels.

When selecting fish, carefully observe them in the tank. Avoid choosing fish with visible lesions, white spots, or damaged fins. If there is a dead fish in the tank, do not select any fish from that aquarium. Make sure the fish are swimming normally—not sideways or erratically. A sick fish can quickly contaminate the entire aquarium population.

It is also recommended that any new fish be quarantined in a separate tank for at least 3 to 4 weeks before introducing it into your established ecosystem.

And there you have it—you’re ready to begin your new adventure!