The Hasa 15501 is a 1 gallon Mini Bulk of Muriatic Acid that's 14.5%. Muriatic Acid is a pool chemical that can be used to maintain pH balance and lower alkalinity in pool water. Muriatic Acid can also be used as a cleaning agent on pool surfaces and tiles. At the end of the pool season, use Muriatic Acid to clear out any mold or algae leftover in your pool.