To lower the alkalinity first make sure the pumps are off and the water is calm. Then premix one ounce of HT pH/Alkalinity Decreser in a small bucket and pour the solution back into the spa, as close to the center as possible and wait just one minute. Then turn all pumps on high speed for 20 minutes and retest the water. Repeat if necessary.
Keep in mind it’s more important for the pH to be accurate then the alkalinity. So, if your reading shows the pH is right on and the Alkalinity is a little off don’t do anything.