To maximize plant growth the pH content 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 pH unstable media - such as rock wool and gravel products - are used and when high plant growth rates destabilize the nutrient mix due to rapid nutrient absorption by the crop. pH Down: Acid formulated using food grade Phosphoric acid. Just add a little at a time if your nutrient pH is too high in order to lower the pH to the proper level.