HTH, 5 LB, PH Increaser, Soda Ash, Raises PH In Pool. Active ingredient-Sodium Carbonate 99.8%-100%. "hth(TM) pH increaser, 5 lbs., raises the pH of swimming pool water. The ideal pH range is 7.2-7.8. Maintaining pH in the proper range will allow your sanitizer to work more effectively, reduce equipment corrosion and reduce skin dryness. "