PH Down is classed as Dangerous Goods: In order to meet freight compliance please order full carton quantities as shown below: PH Down 250ml: 24 per carton. PH Down 1 Litre: 12 per carton. PH Down 5 Litre: 2 per carton All freight orders including Dangerous Goods will be adjusted to full carton quantities. HY-GEN® pH DOWN contains 85% food grade Orthophosphoric acid and will to LOWER the pH when added to your growing system. It’s recommended that you prepare your nutrient solution first and allow it to equilibrate; this can take up to 60 minutes depending on the size of your tank. Always add the required amount of pH DOWN to a small separate container of water and mix well before adding to your nutrient tank.