The COMPOUNDS, CONDITIONS, and PLAYERS INVOLVED"
AMMONIA
There are two forms of ammonia, unionized (NH3) and ionized (NH4+). The unionized form is the only toxic form. An equilibrium exists in water between the quantity of unionized (NH3) and ionized (NH4+) ammonia, with the percentage of the toxic form increasing with increasing temperature and pH values.
For example, at 25 degrees C, in fresh water, less than 0.1% of the total ammonia is in the toxic form, but at pH 8.5 NH3 accounts for more than 10% - an increase of over 100 times. Ammonia is less toxic at lower pH levels. The only way to know how much ammonia is in the toxic unionized form is by determining the pH and temperature and then calculating the percentage of ammonia in the unionized toxic form. (There are tables created for this purpose also.) The long-term safe concentration of ammonia varies with different animal species, but the value of 0.02 mg/L of NH3 is most frequently referenced.