API Pond pH Down slowly lowers the pH of pond water (making it more acidic) without harming delicate pond fish or aquatic plants. The optimal pH for most ponds is 7. 0. Contains sulfuric acid. Slowly lowers the pH of pond waterWill not harm delicate pond fish or aquatic plantsSlowly neutralizes alkaline substances16 oz of pH Down Treats 2,400 GallonsSlowly neutralizes alkaline substances that cause high pH (pH of pond water is affected by mineral leaching, soil runoff and decomposing waste). A high pH limits the ability of aquatic plants to absorb necessary nutrients. Contains no algae-promoting phosphates. Directions: Add 1 teaspoon for every 50 gallons of pond water. Mix this dose in a bucket with 2 gallons of pond water and distribute evenly around the perimeter of the pond. Wait 24 hours, test pH again and repeat the treatment as necessary.