Glossary · 🔄 The nitrogen cycle
New tank syndrome
New tank syndrome is the wave of stressed, sick or dying fish caused by ammonia and nitrite spikes in a tank that was stocked before it finished cycling.
It is not a disease — it is poisoning by the tank's own un-neutralised waste. The classic story is a batch of fish added to a brand-new tank that start dying within a week or two.
Prevention is a proper cycle before stocking; the emergency fix for a tank mid-crisis is frequent partial water changes to keep ammonia and nitrite as close to zero as possible while the bacteria establish.