Status: Critically Endangered
Did You Know: It is estimated that there are fewer than 100 adults in the wild.
Fun Fact: There are over a million Axolotls being taken care of as pets.
The Nitrogen Cycle &
How to Make Your Tank Safe for Axolotls
Updated: Feb 3, 2025
Understanding the Nitrogen Cycle
When setting up a new tank, one of the most important things to understand is the nitrogen cycle. This natural process establishes beneficial bacteria that help keep your tank water safe by breaking down waste. Without a properly cycled tank, toxic compounds can build up and harm or even kill your axolotl.
Why Is the Nitrogen Cycle Important?
Axolotls produce waste just like fish, and that waste breaks down into ammonia—a highly toxic substance that can burn their gills and skin. In a new tank without established bacteria, ammonia builds up quickly and becomes deadly. The nitrogen cycle helps prevent this by introducing good bacteria that convert harmful toxins into less dangerous forms.
How the Nitrogen Cycle Works
The nitrogen cycle consists of three key stages, each driven by different bacteria working together to keep the tank water safe.
1. Ammonia (NH3/NH4+) Formation – The Toxic Beginning
Waste from axolotls, leftover food, and decaying organic material release ammonia into the water.
Ammonia is extremely toxic to axolotls, even in small amounts.
If left unchecked, high ammonia levels cause stress, damage to gills, and even death.
How to Monitor: Use an aquarium test kit to check ammonia levels regularly. Ammonia should always be 0 ppm in a fully cycled tank.
2. Nitrite (NO2-) Conversion – Still Dangerous
Beneficial bacteria called Nitrosomonas start growing in your tank’s filter and surfaces.
These bacteria consume ammonia and convert it into nitrites.
While nitrites are slightly less harmful than ammonia, they are still toxic and can cause stress or gill damage.
How to Monitor: When testing your water, nitrites should also stay at 0 ppm in a stable tank. A spike in nitrites means your cycle is still in progress.
3. Nitrate (NO3-) Formation – The Final Stage
Another type of bacteria, Nitrobacter, forms and converts nitrites into nitrates.
Nitrates are much less toxic than ammonia and nitrites, but they can still be harmful in high amounts.
Safe nitrate levels for axolotls should be below 20-40 ppm.
How to Monitor: Regular testing ensures that nitrates don’t build up to dangerous levels.
4. Removing Nitrates – Keeping Water Healthy
Nitrates don’t naturally break down like ammonia and nitrites, so they must be manually removed.
The best way to keep nitrate levels low is by performing regular water changes (20-30% weekly).
Live plants can also help absorb some nitrates, improving water quality naturally.
Why This Matters: If nitrates build up too much, your axolotl may become lethargic or refuse to eat. Keeping nitrates low ensures a healthy environment.
How Long Does the Nitrogen Cycle Take?
The full cycling process typically takes 4-6 weeks, but it can vary.
During this time, ammonia will spike first, then nitrites, and finally nitrates will appear.
The cycle is complete when ammonia and nitrites are both at 0 ppm, and nitrates stay under 20-40 ppm.
Steps to Cycle Your Tank & Make It Safe for Axolotls
Step 1: Set up Your Tank
Choose a 20-gallon tank or larger for one axolotl.
Use a sponge filter or gentle filtration system to avoid strong currents.
Dechlorinate the water before adding it to the tank.
Step 2: Start the Cycle (fishless cycling recommended)
Add an ammonia source – Use bottled ammonia or let food waste decompose.
Test water parameters – Use an aquarium test kit to monitor ammonia, nitrites, and nitrates.
Encourage beneficial bacteria – Use a filter with biological media and consider adding a bottled bacteria starter.
Step 3: monitor Water Quality
The cycle typically takes 4-6 weeks. During this time, test your water every few days.
You will see ammonia spike first, followed by nitrites, and finally nitrates.
Step 4: Completing the Cycle
Once ammonia and nitrites reach 0 ppm and nitrates stay below 20-40 ppm, the cycle is complete.
Perform a large water change (50%) to lower any excess nitrates.
Your tank is now safe for your axolotl!
Step 5: Ongoing Maintenance
Weekly water changes (20-30%) keep nitrate levels low.
Avoid overfeeding to reduce waste buildup.
Monitor water parameters regularly to prevent issues.
By following these steps, you’ll create a stable, healthy environment for your axolotl, ensuring it thrives in its new home.
For a visual guide on axolotl substrate options, check out this video: Axolotl Substrate Options - Axolotl Care for Beginners
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