The answer depends on your starting pH and TA level, just as it would with adding any other acid or base. However, at a pH of 7.5 and a TA of 100 the answer is about 8 ounces (weight) so 1/2 pound of Borax (sodium tetraborate decahydrate) to raise 10,000 gallons of water by 0.1 pH.Originally Posted by tcjones
That same half-pound of Borax would only raise a pH of 7.0 up by 0.04 while it would raise a pH of 8.0 up by 0.14.
Similarly, at a pH of 7.5, that same half-pound of Borax would raise the pH by 0.12 when the TA was 80 while it would raise the pH by 0.08 if the TA were 120.
Do you have a specific current pH and TA level from which you are starting and that prompted your question? Knowing the CYA level is also helpful (though it's impact is smaller).