It will actually take less than the amounts I indicated, especially for the soda ash, because it will result in carbon dioxide outgassing that will also raise the pH. Figure about 4-1/2 pounds instead of the 8.4 pounds (per gallon of acid). You should mix the soda ash in a bucket of water and then slowly add the acid to it. Wear goggles as there will be bubbling of carbon dioxide when you add the acid and you don't want anything splashing into your eyes.