Urgent · Fish, amphibians, aquatic invertebrates
Aquarium ammonia spike / nitrite poisoning
Any detectable ammonia or nitrite is harmful. Spikes happen with new tanks, overfeeding, filter cleaning, or deaths in the tank.
Immediate safe actions
- Do a 30–50% water change with dechlorinated, temperature-matched water; repeat daily as needed.
- Use a water conditioner rated to bind ammonia/nitrite as directed on the label.
- Stop or reduce feeding for 24–48 hours.
- Remove any dead animals or rotting food. Add aeration.
- Retest every 12–24 hours.
What NOT to do
- Do not replace or deep-clean all filter media at once.
- Do not add more animals.
- Do not chase pH with chemicals during a spike.
Information to gather for the vet
- Ammonia, nitrite, nitrate, pH, temperature
- Tank age and recent maintenance
- Number and size of animals
Red flags
- Ammonia ≥ 1 ppm or nitrite ≥ 0.5 ppm
- Gasping, clamped fins, red gills
- Deaths
Veterinary escalation
- Ongoing deaths or illness after water correction = aquatic vet.
General educational information only. Species differ greatly — always confirm with a licensed veterinarian or animal poison service.