What to do when nitrite spikes

Why nitrite spikes

Nitrite is the middle step of the nitrogen cycle: bacteria turn ammonia into nitrite, and other bacteria turn nitrite into nitrate. During cycling, you often see a nitrite spike after ammonia starts to fall. In an established tank, a nitrite spike usually means the cycle was disrupted.

What to do now

1. Test — Confirm ammonia and nitrite. Log results so you can track progress.
2. Water change — A large partial change (30–50%) with dechlorinated water dilutes nitrite. Repeat as needed until nitrite stays at zero.
3. Reduce feeding — Less food = less waste. Skip a day or two or feed very lightly.
4. Don’t touch the filter — Filter media holds the bacteria that consume nitrite. Rinsing in tap water can prolong the spike.

Quick takeaways

• Water change to dilute nitrite; reduce or skip feeding.
• Don’t rinse or replace filter media in tap water.
• Keep testing until nitrite (and ammonia) stay at zero.