You can correct the pH of a nutrient solution at any time with addition of an acid or a base. Commonly used acids (pH down) are phosphoric acid, sulfuric acid, citric acid and nitric acid. Common bases (pH up) are potassium hydroxide, potassium bicarbonate and potassium silicate. Always use cation when using or handling any of these chemicals as burns and over-corrections are easy to do.
Updated on November 11, 2019