PRO SERIES® 20605PRO 1 gal Dual-Action Algaecide™ is a highly effective fast acting swimming pool algae destroyer. This product kills all types of pool algae: black algae, green algae, and mustard algae. This product is formulated to complement most swimming pool sanitizers. This product is effective and non-staining when used as directed. When used as directed you will see results in 24 hours. PRO SERIES® Dual-Action Algaecide™ is non-foaming and can be used in pools with attached spas or jetted returns.