The Nitrite Spike

What’s Happening

Nitrite is produced as bacteria convert ammonia. It’s toxic because it binds to hemoglobin in fish blood, preventing oxygen transport. Fish may gasp at the surface even in a well-aerated tank.

Steps to Fix It

1. Do a 50% water change with dechlorinated water.
2. Add aquarium salt (1 teaspoon per 5 gallons) if you don’t have scaleless fish or invertebrates — salt ions compete with nitrite at the gill, reducing toxicity. Skip this step if you keep loaches, catfish, shrimp, or snails.
3. Increase surface agitation with an air stone or by adjusting your filter outlet — extra oxygen helps fish cope.
4. Retest in 24 hours. Repeat the water change if nitrite remains above 0.5 ppm.

Prevention

• Avoid adding too many fish too quickly — spikes during cycling are normal.
• Feed less. Every uneaten pellet adds to the nitrogen load.

Track your nitrite readings and get step-by-step crisis alerts in the AquaKeepers app.