What concentration of ammonia is toxic to fish?

Document ID

Document ID TE129

Published Date

Published Date 08/19/2020
What concentration of ammonia is toxic to fish?
Ammonia concentrations toxic to fish
Ammonia exists in water as either the ammonium ion (NH4+) or the un-ionized ammonia (NH3). Un-ionized ammonia is toxic to fish, while the ammonium ion is nontoxic except at extremely high concentrations. At neutral pH 7 and ambient temperature, almost all of the ammonia exists as NH4+. As the pH and temperature increase, the amount of NH3 increases and the amount of NH4+ decreases.

To measure the concentration of un-ionized ammonia in a sample follow the steps provided below:

1. Measure the ammonia concentration using any ammonia method except the free ammonia method
2. Measure pH Measure sample temperature. Reference the table titled “Percentage Un-ionized Ammonia in Aqueous Solution by pH Value and Temperature Calculated from data in Emerson, et. al*” on page 11 in the  FF2 Freshwater Aquaculture Test Kit Manual.
3. Determine the percentage of NH3 using the table, sample pH, and sample temperature
4. Multiply your ammonia concentration by the percent from the table, and then divide by 100.

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