pH Minus. The product size is 2 x 7Kg (Dry Acid). If after testing the water in your swimming pool or spa the pH is too high then use this chemical (sodium bisulphate, Sodium Hydrogen Sulphate) to lower the pH or total alkalinity. Always read and adhere to the instructions on the pack and never directly mix chemicals. Don't forget, the price you see is the price you pay not a penny more. We sell chemicals cheap, not cheap chemicals!