Aquarium Pharmaceuticals Pond pH Down pH Adjuster (16 oz) slowly lowers the pH of pond water (making it more acidic) without harming delicate pond fish or aquatic plants. Optimal pH for most ponds is 7.0. Contains sulfuric acid. Slowly neutralizes alkaline substances that cause high pH (pH of pond water is affected by mineral leaching, soil runoff & 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 treatment as necessary. PondCare pH Down pH Adjuster - pH Adjusters