how chlorophyll-a is affected by pH

For our purposes, we employed a variation on traditional pH Shifting as for our purposes, precipitating the algae proteins and enzymes is not for harvesting them but rather to act as an algicide. Notice how the plant proteins begin to become insoluble, insensitive to light and even damaged as the pH falls, particularly so below a pH of 4.5. 

The CO2 solution’s low pH of 3 precipitates most of the proteins and enzymes in the algae cells, destroying (denaturing) them in the process. Most of the precipitated algae cell contents however dissolve in the CO2 solution's acidic conditions forming extremely minute quantities of non-toxic, carbonate salts that simply rinse off. 

Plants have many proteins and enzymes, but chemically, all but one, chlorophyll-a, become unstable at a pH below 4. Although most plant enzymes are insoluble below a pH of about 4, chlorophyll-a remains viably active as low as pH 2!