The HTH .34 Gallon Algae Guard 3X Concentrated Formula is 3 times stronger than the original HTH Algae Guard. Use 1/3 as much to treat the same amount of water. 30-percent Strength. Prevents Green, Black and Yellow Algae. Non-Foaming Formula. Active Ingredient-Quarternary Ammonium Compounds, Benzyl-C12-18-Alky 13-17-percent.