pH plays an important role in your swimming pool or hot tub.  For example, chlorine only works optimally at a specific pH range (usually regarded as 7.2-7.6).  Too Low, and your chlorine works too well, which is harmful to people, your pool's surface, and equipment.  Too High, and your chlorine stops working.

If your pH is too high (which is the most common case), pH Decreasers will lower your pH.

If your pH is too low, pH Increasers will raise your pH.

Also remember to keep your Alkalinity in the correct range, as it helps to keep pH from bouncing around too rapidly (called a Buffer).  Your pH will increase whenever you raise your Alkalinity, which may require additional pH adjustments.  Because of the close relationship to pH, we have included Alkalinity Increasers here as well.

Generally for balancing water, we recommend adjusting Alkalinity first, then after waiting enough time for the product to fully get mixed into the water (usually 15 minutes for running hot tubs and 4 hours for running swimming pools) adjust the pH second.