pH stabilization testing is performed when a significant pH drift is observed in the routine trout toxicity test.
pH drift can occur when dissolved CO2 dissipates from the test solutions due to aeration. An upwards drift in pH can cause artificial toxicity if there is ammonia present in the sample. Ammonia exists primarily in its ionized form at low pH, but as pH increases more ammonia exists in unionized form, which is extremely toxic to trout.
For wastewater samples in particular, if the routine trout test (EPS 1/RM/13 - performed as either a 100% screen or as an LC50), has a mortality rate in excess of 50% in the full strength sample, it confirms that ammonia is present in the sample. If there is documentation of pH drift during the test, it is possible trout mortality may be reduced when the sample is run with the pH stabilization manipulation.
The pH stabilization manipulation can be run as an LC50 (multi-concentration) or as a screen (100% only).