Leslie's Algae Control is a 60% concentrated polyquat pool algaecide effective at preventing and treating most forms of algae growth in swimming pools and spas. Leslie's Algae Control is a versatile algaecide that is effective at preventing and treating most forms of algae in swimming pools or spas. It's particularly useful in helping prevent more stubborn algae such as mustard/yellow algae from growing. Keeping the water sanitized, having proper filtration and circulation as well as balanced water chemistry levels are key when it comes to preventing algae. If you are away for a short period of time, adding a polyquat algaecide like Leslie's Algae Control helps prevent algae if your chlorine sanitizer level gets too low. Algae Control is compatible with saltwater chlorinated pools as well. Since Algae Control is non-metallic or contains no metals, it will not cause staining like some other algaecides potentially can.