The pH of the nutrient solution affects plants' ability to absorb some of the nutrients. The optimal pH level varies among plants, but for most plants a pH between 5.5 and 6.0 provides the best results. When the pH rises above 6.5, some nutrients will fall out of solution and solidify on the floor and walls of the container, no longer available to the plant. Dilute acid solutions, known as "pH down," are available for reducing the pH in the hydroponic system when needed. Using a commercial pH down solution is safer than using concentrated acid.
Mix the nutrient solution thoroughly into the water as directed on the container using a wood or plastic spoon or paddle. When using two part solutions, thoroughly mix between additions.
Check the pH of the solution after mixing. Use a pH test kit or pH meter to obtain an accurate reading.
Add a few drops of pH down solution per gallon of nutrient solution if the pH is above the desired level. Mix well and check the pH again.
Continue adding pH down, a few drops at a time, until reaching the desired pH. Mix thoroughly after each addition.
Check the pH every day or two. The pH will usually increase as the nutrients are used by the plants. Adjust the pH again as needed.