Two 250ml (8oz) of pH Down (16oz in total) Great for Aquaponics and Hydroponics Use 15mL (1 tbsp) per gallon or 3ml per Liter This hydroponic solution does not need to be diluted. The Atlas Scientific pH Down is simple to use and straight to the point. Use this product sparingly. Before you begin adding Down up to your water or soil, test the pH to confirm that you need to lower the pH level.