Hasa 72041 1 gal Algi-Control - Hasa Algi-Control is quaternary ammonium algaecide (quat) that is efficient, economical and stable when used in proper dilution. It is compatible with most chemicals used in pool water and will not damage tile, concrete, metal, or plastics. It keeps pool water sparkling, clear, and free of visible green and blue-green algae, slime and green brown colors.