Nitrite in an Aquarium – Immediate Water Checks

What to check first

• Perform an appropriate partial water change and condition replacement water.
• Increase aeration and confirm filter operation.
• Continue monitoring ammonia and nitrite.

What you can do now

• Perform an appropriate partial water change.
• Condition replacement water.
• Increase aeration.
• Confirm the filter is working.
• Reduce feeding temporarily.
• Avoid replacing all biological media.
• Continue monitoring ammonia and nitrite.

What may be contributing

• An immature or disrupted biological filter
• A recent filter or stocking change

Questions that help narrow the problem

Are fish gasping, very inactive or otherwise distressed?

Yes · No · Not sure

Was the aquarium, filter or biological media recently started, cleaned or changed?

New aquarium · Filter or media changed · No recent change · Not sure

Would you like to enter the exact nitrite and other water-test results?

Yes · No

Relevant tests and product guidance

These links come from the existing troubleshooting record. They do not replace water-quality correction or the current product label.

• API Nitrite NO2 Test Kit
• API Ammonia Test Kit
• Seachem Stability
• API Stress Zyme
• Seachem Prime

Avoid for now

• Avoid replacing all biological media.
• Avoid relying on a product instead of correcting the filter and water issue.