The nitrogen cycle in aquariums is crucial for maintaining a healthy environment for fish and other aquatic life. Here’s a detailed overview of how it works:

Fish waste, uneaten food, and decaying plant matter produce ammonia (NH₃), which is highly toxic to aquatic life.

In an aquarium setting, nitrogen fixation is less significant compared to natural ecosystems. Instead, the focus is on how ammonia is processed by beneficial bacteria.

This is a two-step process carried out by beneficial bacteria that colonize the filter media and substrate.

• Bacteria: Nitrosomonas converts ammonia (NH₃) into nitrite (NO₂^-).
• Significance: Nitrite is also toxic to fish but less so than ammonia.

• Bacteria: Nitrobacter converts nitrite (NO₂^-) into nitrate (NO₃^-).
• Significance: Nitrate is less harmful and can be used by plants as a nutrient.

• Water Changes: Regular water changes help lower nitrate levels.
• Live Plants: Aquatic plants can absorb nitrates as a nutrient.
• Denitrifying Bacteria: In anaerobic environments (like deep substrate or special filters), some bacteria can convert nitrate back to nitrogen gas (N₂), releasing it into the atmosphere.

When setting up a new aquarium, it undergoes a “cycling” period to establish beneficial bacteria.

• Fishless Cycling: Adding ammonia manually to feed bacteria.
• Fish-in Cycling: Adding a small number of fish to introduce waste, though this can stress fish.

• Testing: Regularly test water parameters (ammonia, nitrite, nitrate) to monitor the cycle.
• Beneficial Bacteria: These bacteria take time to establish. Patience is crucial during the cycling process.
• Toxic Levels: Aim for ammonia and nitrite levels at 0 ppm, and keep nitrates below 20-40 ppm for a healthy aquarium.
• By understanding and managing the nitrogen cycle, you can create a stable and healthy environment for your aquatic life.