The alkalinity in pool water should be no higher than 120. Because alkalinity tends to be a buffer for the pH, it's rare that I see high alkalinity and low to normal pH although it CAN happen. The alkalinity can be lowered using muriatic acid with the problem being that it also lowers the pH at the same time. The answer is to use both muriatic acid along with sodium CARBONATE also known as soda ash (Do not confuse with sodium BI-carbonate which raises alkalinity) Depending on how high the alkalinity is, add the desired amount of muriatic acid and let circulate for several hours. Once the alkalinity is within the desired range, you will use pH increaser (soda ash) to bring the pH back up without raising the alkalinity. Keep in mind that it doesn't take much soda ash to increase pH.