Typically Pottasium Hydroxide is used to raise the pH. A carbonate such as magnesium carbonate or pottasium carbonate as a buffer. Lowering the pH is usually done with Phosphoric acid or Nitric Acid. Dyna-Grow pH Up contains Pottasium Hydroxide and Pottasium Carbonate. Dyna-Grow pH Down usually contains both Phosphoric acid or Nitric Acid. Cheaper versions usually do not add the buffer (pottasium carbonate) to their pH Up, nor do they add Nitric Acid to their pH down.