Halt® 50 Algaecide Algae’S Worst Enemy! Rely On Concentrated Halt® 50 Algaecide To Kill And Prevent All Types Of Algae. A Single Quart Of This Super Concentrated Swimming Pool Algaecide Treats Up To 240,000 Gallons — A Great Value! Plus, This Non-Metallic, Low-Foaming Formula Will Not Stain Or Discolor Hair. Swim Immediately After Treatment. Great For All Pool Types. Maintenance Dosage: 1-1/3 Oz. Per 10,000 Gallons. Buy 4 Quarts And Save!