Algae Culture and pH

By Matthew Huber and Katie Blaha-Robinson


              The pH in water measures how acidic or basic that water is. Anyone who has ever maintained a pool can attest that monitoring pH is incredibly important. This is because pH affects nearly every biologic and chemical process, especially aquatic organisms like algae. So, what do we need to know? Well, we need to understand water. Each water molecule, H2O, is made up of two hydrogen atoms and one oxygen atom. As a molecule, water is not an ion because it does not have a negative or positive charge. However, if a water molecule breaks up into H+ and OH-, ions are formed.



 Water molecules in pH

How do we measure pH?

 A measurement of pH is determined by the concentration of H+, or hydrogen ions within the water. Specifically, pH is represented as the negative log of the hydrogen ion concentration, -log [H+]. An acid will have many H+ ions, while a base will have many OH- ions. The pH scale is from 0 to 14, with pH 7 representing an equal balance of H+ and OH- ions.  This value, pH 7, is neutral. Values below 7 are considered acidic and above 7, bases. The ocean’s pH is around 8.2, although addition of CO2 into our atmosphere is causing the pH of the world’s oceans to drop (Ocean Acidification).

pH colors




How is pH important for algae?


Now that we have an understanding for pH, how does this impact algae culturing? First, different algae cultures may have different pH ranges and finding that optimal pH environment can help your algae cultures, not only survive, but also thrive. For example, marine algae strains prefer pH usually around 8.2, while freshwater strains prefer pH around 7.0.  Meanwhile, spirulina (Arthrospira) prefers a pH of around 10.

pH and algae culture

Second, algae require carbon dioxide, for growth and pH can affect how much is available. When carbon dioxide dissolves into water, it can exist as one of three different species, depending on pH of the water. Carbon dioxide (CO2) is found at low pH, bi-carbonate (HCO3-) at neutral pH, and carbonate (CO32-) at high pH. Algae cannot use carbonate, only carbon dioxide and bi-carbonate. A high pH range will prevent your algae from doing photosynthesis, hurting culture growth. So, monitoring and understanding the pH environment of your algae culture is incredibly valuable.

carbon dioxide, bicarbonate, and carbonate as a function of pH



 U.S Geological Survey. “pH—Water properties”. The USGS Water Science School. 02 Dec, 2016. Web,<>.

 Fondriest Environmental, Inc. “pH of Water.” Fundamentals of Environmental Measurements. 19 Nov. 2013. Web. < >.