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SESK: Stuff Everyone Should Know · sesk.info/fish-ammonia-toxicity

Which form of ammonia is far more toxic to fish?

Un-ionized ammonia (NH3), about 100 times more toxic than ammonium.

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  1. Un-ionized ammonia (NH3) ✔
  2. Ionized ammonium (NH4+)
  3. Both are equally toxic

Why: Un-ionized ammonia is about 100 times more toxic than ammonium. Its share of the total rises as pH and temperature rise.

Huh, didn't know that: Ammonia has no color and no smell, even at levels that hurt fish, so only a test can find it.

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Why did the fish get bad grades? Because it was below sea level.
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References

Answer: Un-ionized ammonia (NH3). Un-ionized ammonia is about 100 times more toxic than ammonium. Its share of the total rises as pH and temperature rise.

  1. UF/IFAS Extension FA031: Ammonia in Aquatic Systems edis.ifas.ufl.edu/publication/FA031
    it is approximately 100 times more toxic to fish than the ionized (NH 4 + ) form.
    Checked 2026-10-11.
  2. UF/IFAS Extension FA031: Ammonia in Aquatic Systems edis.ifas.ufl.edu/publication/FA031
    Ammonia is colorless and, even at levels toxic to fish, odorless.
    Checked 2026-10-11.

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