Microalgal consumption of CO2 in batch culture systems (without added CO2) will increase the pH, and levels above pH 9 are toxic to many microalgal species (cyanobacteria generally have higher tolerances for elevated pH which may give them a competitive advantage under such conditions). Buffers may give some control over the rise in pH and are suitable to low volume stock cultures, however in large scale dense cultures pH control is probably more readily met by the addition of CO2 back into the culture by aeration (air only or air/CO2 mix ..see Carbon).
TRIS buffer (tris (hydroxymethyl) aminomethane): Generally TRIS is used at concentrations up to 5 mM but some microalage find it toxic. An example of varying susceptibility is shown by a comparison between two frewshwater cyanobacteria, Microcystis and Anabaena. TRIS at 10 mM provides good buffering between pH 7.4-7.7 in Microcystis; with increased tolerance towards supraoptimal concentrations of monovalent but not divalent cations (McLachlan and Gorham, 1961). However TRIS is toxic in Anabaena flos-aquae at concentrations too low to provide suitable buffering but filament coiling, indicative of good growth, is promoted by addition of 1 mM TRIS (Gorham et al, 1964).
Glycylglycine: is used at concentrations up to 3.8 mM, however it is both expensive and rapidly metabolised by bacteria and should only be used in axenic cultures
Sodium bicarbonate (NaHCO3): buffers well in the pH range 7.5-8.5 and is used in the freshwater medium MLA for cynaobacteria cultures.