pH Control:

pH is usually controlled at pH 4.5 to 5.0. This usually requires the addition of base only. Ammonium hydroxide is the base of choice as it also servers as an alternate nitrogen source. The combined basal salt media and trace salts have a tendency to precipitate out of solution above pH 5.0, which interferes with cell density measurement and reduces salts available to the cells.

Off-line pH measurements should be done daily to ensure probe malfunction or drift has not occurred.