conducted from the beginning of the logarithmic phase. When compared with the logarithmic phase, the effect of pH on the growth of M. aeruginosa was less remarkable when acidification treatment was conducted during the stable breeding phase. There- fore, the method of CO2 acidification is much more applicable for the prevention of blue-green blooms in lakes than for the removal of algae after algal blooms have already occurred. It was also found that different blue-green algae species responded differently to the same acidic condition.