Emergency steps (do these now)
- Do a 30–50% water change with dechlorinated, temperature-matched water. This is the fastest way to dilute ammonia. Repeat daily while it stays high.
- Stop feeding for 24–48 hours. Fish are fine; uneaten food and extra waste are making it worse.
- Add a detoxifier (ammonia binder like Prime/Amquel) to neutralize what's left between water changes. It buys time — it doesn't replace changes.
- Boost aeration — an airstone or a bubbling filter return. Ammonia is more toxic when oxygen is low and pH is high.
- Remove the source — uneaten food, a dead fish, a rotting plant, or too many fish for the filter.
What NOT to do
- Don't change or rinse your filter media in tap water — that's where your beneficial bacteria live. Chlorine kills them and ammonia spikes harder.
- Don't add more fish until ammonia and nitrite read zero.
- Don't overdose chemicals hoping for a shortcut — water changes are safer and more effective.
Why it spiked in the first place
Ammonia comes from fish waste and decaying matter. In a healthy tank, beneficial bacteria convert it to nitrite and then to far-less-toxic nitrate — the nitrogen cycle. You get an ammonia spike when that bacteria colony can't keep up:
- New tank syndrome — the tank isn't cycled yet and has no bacteria colony. This is the most common cause.
- Overstocking or overfeeding — more waste than the filter can process.
- A crashed colony — from cleaning filter media too aggressively, a medication, or a long power outage.
Stop it coming back
Cycle every new tank before adding fish, stock slowly, feed only what's eaten in a couple of minutes, and test regularly — ammonia problems are silent until a fish is already in trouble. Logging your parameters means you catch the climb on day one, not the day a fish dies.
TankMate logs ammonia, nitrite, nitrate and pH in seconds, charts the trend, and flags danger early with a Tank Health Score — and if a fish already looks sick, you can photograph it for an AI read against those same numbers. It's free on iOS and Android.