For many owners, seeing an aquarium fish die suddenly when it seemed healthy the day before is a frustrating and sad experience. This phenomenon often has an explanation, even if it's not immediately visible to the naked eye. In most cases, the cause lies... in the water.
Illustration image Pixabay
Water quality is a vital factor for fish. In the wild, rivers, lakes, or seas have a relatively stable chemical balance. In an aquarium, this balance is more fragile. An excess of organic waste (food leftovers, excrement, dead leaves) leads to the accumulation of toxic substances like ammonia and nitrites, invisible to the naked eye but potentially deadly. A rapid change in these parameters can kill a fish within hours.
Temperature also plays a crucial role. Each fish species has an ideal temperature range. Water that's too cold or too hot weakens their immune system, making them vulnerable to diseases. Sudden changes, for example during a water change, can cause thermal shock.
Other invisible factors include:
- Unsuitable pH (water acidity) for the species.
- Insufficient oxygenation, often due to poor water circulation or overcrowding.
- The presence of heavy metals or chemicals (sometimes from tap water or cleaning products used near the aquarium).
- Diseases or parasites introduced by new fish or plants without prior quarantine.
Sometimes the problem stems from prolonged stress. An aquarium that's too small, a noisy environment, aggressive tankmates, or unsuitable decorations can exhaust fish, weakening their resistance to infections.
A fish that "dies for no reason" has often fallen victim to an invisible but very real imbalance. Prevention involves regular maintenance, frequent water testing, a population suited to the aquarium or pond's volume, and stable conditions.