Acidity versus alkalinity are key factors in your crop?s water and root zone, as measured by pH. If you have too high or too low pH, your crops cannot uptake nutrients, and may well be damaged or even killed. That?s why smart growers daily monitor and adjust optimum pH levels for hydroponics, sphagnum moss, coco coir, rockwool, aeroponics, soil, and other types of plant growth media. Some companies make cheap, inferior pH adjustment products that never achieve consistent results; some of those products contain harmful materials. Advanced Nutrients pH products are carefully-manufactured pure concentrates that are pharmaceutical grade. Ingredients: Phosphoric Acid WARNING: DO NOT STORE pH UP AND pH DOWN SIDE BY SIDE! Available in 1L and 4L sizes.