How much soda ash would you add to a 125000 gallon pool to raise pH from 6.8 to 7.2?

Answer 1

A normal 20,000 gallon will require 2 1/2 lbs. of Sodium Bicarb. (40 oz.) to raise the pH about .1ppm. So for a 125,000 gallon pool you would use about 240 oz. of Bicarb., or about 14 lbs. I know soda ash is a bit more effective, but this sould give you a good starting point.

Remember to work your way up, not down. It's easier to add chemicals than take them away.

You should be running your pH between 7.6-7.8, not 7.2. It's too low, you'll use too much acid to keep it there, and the index most "pool experts" use is based upon your local water company's index, not an actual swimming pool index.