The Nitrogen Cycle: Essential for an Axolotl Aquarium

Before welcoming an axolotl into its aquarium, it is essential to understand how the nitrogen cycle works. This biological process, often ignored by beginners, is the foundation of a stable and healthy environment for any aquatic animal. A poorly managed cycle can lead to water poisoning and even the death of your axolotl.

What Is the Nitrogen Cycle?

The nitrogen cycle is a natural process that transforms waste produced in the aquarium (excrement, uneaten food, decaying leaves…) into less toxic compounds thanks to the action of beneficial bacteria. It occurs in three main stages:

1. Ammonia (NH3/NH4+): produced directly by waste and organic matter. It is highly toxic, even in small amounts.
2. Nitrites (NO2-): formed by the transformation of ammonia by nitrosomonas bacteria. Also toxic.
3. Nitrates (NO3-): nitrites are then converted into nitrates by nitrobacter bacteria. Less dangerous, but must be removed through water changes.

This cycle is invisible to the naked eye, yet vital for keeping the water non-toxic. Without it, waste accumulates and quickly poisons the axolotl’s environment.

Why Is It So Important for an Axolotl?

Axolotls are particularly sensitive to water quality. They breathe through their gills, skin and lungs. High concentrations of ammonia or nitrites can cause:

• Burns on the gills
• Lethargy or extreme agitation
• Weakened immune system
• Death in case of prolonged toxic spikes

Placing an axolotl in an uncycled aquarium exposes it directly to dangerous substances. The nitrogen cycle is a basic requirement, not an option.

How to Establish the Nitrogen Cycle

The cycle develops gradually and can take 3 to 6 weeks. Here’s how to proceed:

1. Set up the tank: substrate, dechlorinated water, filter running
2. Add an ammonia source: fish food, pure ammonia (fishless cycling), or introduce snails
3. Let it run without animals: this is essential!
4. Test the water regularly: using liquid test kits (more reliable than strips)

The cycle is considered complete when ammonia and nitrites reach zero and nitrates begin to appear. That is the sign that beneficial bacteria are established.

The Crucial Role of the Filter

The bacteria responsible for the nitrogen cycle do not float freely in the water: they colonise porous surfaces, especially the biological media inside the filter (sponges, ceramic rings…). Without filtration — or if the filter is cleaned too harshly — these bacteria die and the cycle collapses.

Practical tips:

• Never rinse filter media under tap water (chlorine = kills bacteria)
• Never replace all filter media at once
• Let the filter run 24/7 without interruption

How to Know if the Water Is Cycled

Only regular testing can confirm it. Signs of a completed cycle include:

• Ammonia = 0 mg/L
• Nitrites = 0 mg/L
• Nitrates = between 5 and 40 mg/L (acceptable for an axolotl)

A tank with no nitrates is not cycled. A tank with measurable ammonia or nitrites is potentially toxic. These tests should be done using liquid kits (JBL, API), far more accurate than strips.

Common Mistakes to Avoid

• Introducing an axolotl before the cycle is complete
• Changing 100 % of the water without precaution
• Cleaning the filter with hot or chlorinated water
• Forgetting to test water parameters regularly

A poorly managed cycle leads to nitrite or ammonia spikes, often deadly within hours. Always prepare the environment before introducing any living creature.

What to Do in Case of a Problem

If you detect an ammonia or nitrite spike:

• Immediately change 30–50 % of the water with dechlorinated water
• Add bottled bacteria to help (optional but useful in emergencies)
• Reduce feeding temporarily

Setting up a secondary backup tank may be useful if levels are too high, allowing you to temporarily move your axolotl.

Conclusion

The nitrogen cycle is the cornerstone of any healthy aquarium. Without it, it is impossible to ensure an axolotl’s long-term survival. By understanding and respecting this natural biological process, you provide your aquatic companion with a stable, non-toxic habitat that supports a long and peaceful life.

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