pH up and pH down: Keep the nutrient solution and the growing medium in the sweet spot (pH 5.56.5) for optimal nutrient uptake and no nutrient deficiencies. pH Up and Down are buffers composed of a weak base (Up) and weak acid (Down) designed to correct pH imbalances. pH Up and pH Down adjust the pH for optimal nutrient uptake and stable beneficial bacteria colonies, and they forestall nutrient deficiencies.