To prevent pool algae, algaecides play an important role. They can be used as an algae-cide to kill small, isolated blooms, but most perform best as an algae-stat, to control and prevent pool algae growth. Pool algaecides are formulated to kill all algae types, but some control certain strains of pool algae better than others, and different algaecides each have their own way of controlling algae.