Check the listing for details. General Hydroponics pH Down Liquid - 1 Quart Garden Meter. Condition: New. Listed at 24.56 USD. The Acid formulation uses food grade Phosphoric acid to lower the pH to the proper level. To maximize plant growth, the pH of your nutrients should be slightly acidic. Experienced growers consider the ideal pH for most crops to fall between 5.5 and 6.5. Users of General Hydroponics nutrient products generally do not experience problems maintaining the proper pH range because our formulas are pH buffered. However, some important exceptions do exist. Acid content can reach unacceptable levels when nutrient solutions are mixed with poor quality water, or when pH unstable media ”“ such as rock wool or gravel products ”“ are used, or when high plant growth rates destabilize the nutrient mix due to rapid nutrient absorption by the crop.