Important aquarium checks
Nitrite in an Aquarium – Immediate Water Checks
See water-first actions for a high aquarium nitrite reading, including water changes, aeration, biological filtration and continued testing.
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.
Avoid for now
- Avoid replacing all biological media.
- Avoid relying on a product instead of correcting the filter and water issue.