GH pH DownIn Store Location: A9 GH pH Down This concentrated solution from General Hydroponics is basic equipment for any hydroponic system. pH levels in water vary greatly from water source to water source. Different plants respond positively to different pH levels. Most plants need pH levels between 5. 5 and 6. 8. Add General Hydroponics pH Down to your nutrient solution to lower pH. Available in quart and gallon sized bottles!