What concentration of ammonia is toxic to fish?

Document ID

Document ID TE129


Version 2.0


Status Published

Published Date

Published Date 25/01/2018
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,“Percentage of Un-ionized Ammonia in Aqueous Solution Table” from FF2 Freshwater Aquaculture Test Kit Manual.
3. Determine the % 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.