Water guide
Nitrite in Fish Tank: Why It Spikes and How to Bring It Down
Last updated: May 2026
Target
- Wanted reading: 0 ppm nitrite for virtually all ornamental freshwater setups.
- Classic story: Nitrite climbs mid-cycle or after biofilter shock while ammonia finally falls.
- Front-line tool: Temperature-matched water changes plus reduced feeding.
Why nitrite appears
Nitrite is the intermediate stage between ammonia oxidation and stable nitrate production. Any event that knocks nitrite-oxidising bacteria (new tank, deep substrate disturbance, medication) can let it climb again.
Salt mention (carefully)
Chloride competition can mitigate acute nitrite stress for some fish, but species tolerance varies—never guess concentrations without species homework.
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