The pH of a nutrient solution is a measurement of its relative concentration of positive hydrogen ions. Negative hydroxyl ions are produced by the way systems filter and mix air into the nutrient solution feeding plants. Plants feed by an exchange of ions. As ions are removed from the nutrient solution, pH rises. Therefore, the more ions that are taken up by the plants, the greater the growth. A solution with a pH value of 7.0 contains relatively equal concentrations of hydrogen ions and hydroxyl ions. When the pH is below 7.0, there are more hydrogen ions than hydroxyl ion. Such a solution “acidic.” When the pH is above 7.0, there are fewer hydrogen ions than hydroxyl ions. This means that the solution is “alkaline.”
Test the pH level of your nutrient with a kit consisting of vials and liquid reagents. These kits are available at local chemistry, hydroponic, nursery, garden supplier, or swimming pool supply stores. It is also a good idea to test the pH level of your water before adding any nutrients. If your solution is too alkaline add some acid. Although such conditions rarely occur, sometimes you may have to reduce the level of acidity by making the solution more alkaline. This can be achieved by adding potassium hydroxide (or potash) to the solution in small amounts until it is balanced once again.
–Charles E. Musgrove