Understand the cycle stage
Nitrite is produced as ammonia is processed and is later converted by other microorganisms. A detectable reading can mean the biological filter is not yet handling the load reliably.
New tanks, power interruptions, or replacing filter media can disrupt this process. Test both ammonia and nitrite rather than relying on a single parameter.
Protect the colony
Confirm an unexpected result with a fresh test and review feeding and recent maintenance. Maintain aeration and seek experienced help for a safe water-change plan.
Do not add shrimp while nitrite remains detectable in a cycling setup. A calendar estimate cannot substitute for test results.
For your own tank
During cycling, continue testing until the system processes waste reliably rather than relying on a single zero reading. After a filter disruption or large stocking change, test again. Keep livestock out of a tank that still shows detectable nitrite.
Use these as general hobby references. Test your aquarium and confirm product guidance before making changes.