Final answer:
Muriatic acid or sodium bisulfate can be used to lower alkalinity in a pool. Dilute muriatic acid before use. Exercise caution when handling muriatic acid as it is unsafe.
Step-by-step explanation:
To lower alkalinity in a pool, you can use muriatic acid. However, it's important to exercise caution when handling this acid as it is unsafe. Muriatic acid should be diluted before use to lower its concentration to a safer level. It is commercially available at concentrations of about 18%.
If the pH of the pool water is high, you can use liquid HCl or sodium bisulfate to lower it. The bisulfate anion in sodium bisulfate can partially dissociate in solution, helping to lower the pH. The exact amount of muriatic acid or sodium bisulfate needed to lower the alkalinity will depend on the current alkalinity level of the pool water.