An emergency fish-in cycle is a method of establishing the nitrogen cycle in an aquarium while fish are present. This is typically done when there is an urgent need to add fish to an aquarium, such as when rescuing fish from a sick or dying tank.

Steps for an Emergency Fish-In Cycle

1. Prepare the Aquarium

• Setup: Ensure the aquarium is properly set up with a filter, heater, and substrate. Add water and any necessary decorations or plants.

2. Add Fish Gradually

• Introduction: Introduce only a few fish at a time to avoid overwhelming the biological filter. Start with hardy species that are tolerant of higher ammonia and nitrite levels.

3. Monitor Water Parameters

• Testing: Test the water daily for ammonia, nitrite, and nitrate levels. Ammonia and nitrite should be kept as close to 0 ppm as possible, while nitrate should be below 20 ppm.

4. Perform Partial Water Changes

• Water Changes: Perform 25-50% partial water changes every other day to remove excess ammonia and nitrite. Use a water conditioner to neutralize chlorine and chloramines.

5. Add Beneficial Bacteria

• Bacteria Introduction: Introduce beneficial bacteria to the aquarium through products such as live bacteria cultures or bottled bacteria supplements. These bacteria will help break down ammonia and nitrite into less harmful nitrates.

6. Feed Lightly

• Feeding: Overfeeding can increase ammonia levels. Feed fish small amounts several times a day instead of one large meal.

7. Be Patient

• Patience: The fish-in cycle can take several weeks or even months to complete. Monitor water parameters closely and adjust water changes and feeding as needed.

Tips for a Successful Fish-In Cycle

• Hardy Fish Species: Use hardy fish species, such as tetras, guppies, or mollies.
• Low Population: Keep the fish population low during the cycle.
• Live Plants: Add live plants to help absorb nitrates and provide oxygen.
• Avoid Chemicals: Avoid using harsh chemicals or medications during the cycle.
• Monitor Fish: Monitor fish closely for signs of stress or illness.

Important Note

A fishless cycle is the preferred method for cycling an aquarium, as any amount of ammonia is toxic to fish and other live animals. However, in situations where a fish-in cycle is necessary, following these steps can help minimize stress and harm to the fish while establishing the nitrogen cycle.