Why it matters
Nitrite binds to fish hemoglobin, preventing oxygen transport. Symptoms are gasping at the surface and brown gill tissue.
Ideal ranges
| Water type | Ideal | Acceptable |
|---|---|---|
| Freshwater aquarium | 0.0 | — |
| Saltwater / reef | 0.0 | — |
| Koi pond | 0.0 | — |
How to test
- 1
Use a liquid test kit
API and Salifert nitrite kits are reliable. Strips work but read low.
- 2
Test daily during a new cycle
Nitrite spikes typically appear 1 to 3 weeks after ammonia drops to zero.
How to correct high nitrite
Add aquarium salt at 1 tablespoon per 5 gallons
Chloride competes with nitrite at the gill, blocking absorption. Skip in tanks with salt-sensitive plants or fish.
Water change 30 to 50 percent
Repeat daily until nitrite reads zero.
Reduce feeding
Less waste in means less ammonia, which means less nitrite.
Common causes
- •Cycling tank
- •Filter crash
- •Antibiotics killing bacteria
- •Sudden bioload increase
FAQs
Should I do water changes during the nitrite spike?
Yes if fish are present. The old advice to let it run was for fishless cycling only.