Caring for an aquarium is not only an aesthetic pleasure, but also a responsibility for the health of its inhabitants. One of the key aspects of maintaining a stable aquarium environment is regular water testing. But which tests are really mandatory? Let's break down which parameters need to be monitored and why it's important.

1. pH - water acidity

pH determines the level of acidity or alkalinity of the water, which directly affects the comfort and survival of fish, plants and other inhabitants. For most freshwater aquariums, the normal pH range is between 6.5 and 7.5, but this can vary depending on the species of fish (for example, cichlids prefer a more alkaline environment). Testing the pH is important to avoid sudden fluctuations that can stress the inhabitants.

How often should I test? Once a week, and more often when starting a new aquarium or after significant changes (e.g. adding decorations).

2- Ammonia (NH3/NH4+)

Ammonia is one of the most toxic products of fish life and decomposition of organic matter. Even small amounts can be fatal. In a healthy aquarium with an established biological cycle, ammonia levels should be close to zero. This test is especially important in new aquariums where the nitrogen cycle is not yet established.

How often should I check? Daily in a new aquarium, then every 1-2 weeks after stabilisation.

3. nitrites (NO2-)

Nitrites occur during the conversion of ammonia by bacteria. They are less toxic than ammonia, but still dangerous to fish. High nitrite levels can indicate filtration problems or overfeeding. Ideally, their concentration should also tend towards zero.

How often should I check? Once a week or when water quality problems are suspected (e.g. turbidity or fish kills).

4. Nitrates (NO3-)

Nitrates are the end product of the nitrogen cycle. They are less harmful than ammonia and nitrite, but their accumulation can lead to algae growth and poor fish health. The norm for most aquariums is up to 20-40 mg/litre, although for some sensitive species it is better to keep below 10 mg/litre.

How often should I check? Every 1-2 weeks, especially if you notice increased algae growth.

5. Water hardness (GH and KH)

Total hardness (GH) indicates the amount of dissolved minerals such as calcium and magnesium, while carbonate hardness (KH) is responsible for the water's ability to maintain a stable pH. These parameters are important for the health of fish and plants, as well as preventing sudden spikes in acidity.

How often should I check it? Once a month if your aquarium water is stable, or more often when using new water (e.g. from another source).

6. Temperature

Although this is not a chemical test, controlling water temperature is critical. Different species of fish require a certain range of temperatures (e.g. tropical fish are comfortable at 24-28°C). Abrupt temperature changes can cause stress or disease.

How often should I check? Daily with a thermometer.

Additional tests (as required)

• Phosphates (PO4): Important if you are fighting algae, as excessive amounts can stimulate growth.
• Iron (Fe): Useful for aquariums with live plants to keep an eye on nutrient levels.
• Salinity: Necessary for marine or brackish aquariums.

How to do the tests?

Aquarium test kits are convenient for testing water: drop kits (more accurate) or strips (quick but less reliable). Follow the manufacturer's instructions and take measurements at the same time of day for consistent results.

 

Why it's important.

Regular testing helps to detect abnormalities and prevent problems ranging from massive fish kills to uncontrolled algae growth. Healthy water is the key to a long and happy life for your aquarium.

Conclusion

For basic aquarium care, be sure to monitor pH, ammonia, nitrite, nitrate, and temperature. If you keep plants or specific fish species, add hardness tests and, if necessary, phosphates or iron. The key is regularity and attention to detail. Your aquarium will thank you with bright colours and active inhabitants!