How much Borax to raise pH?

[tcjones]

What is the calculation for Borax and raising pH in pounds of Borax per10,000 gal per pH 0.1 units?

[chem geek]

What is the calculation for Borax and raising pH in pounds of Borax per10,000 gal per pH 0.1 units?

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.

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).

Richard

[Simmons99]

Well I used 4 lbs of Borax on a 14,000 gallon pool with the TA at 120 - I will test again tonight - but preliminary tests raised it from below 6.8 to ~7.0.

[chem geek]

Well I used 4 lbs of Borax on a 14,000 gallon pool with the TA at 120 - I will test again tonight - but preliminary tests raised it from below 6.8 to ~7.0.

My calculations show that this would raise the pH from 6.8 to 6.95 which is in the ballpark of what you found.

If you wanted to continue to raise it to 7.4, you would need to add 133 ounces (8 pounds, 5 ounces) more. Also, doing this increases your alkalinity so your TA would then be 147.7 and you'd probably want to lower that, THEREFORE I suggest that you follow Ben's Lowering Your Alkalinity procedure first while you still are at lower pH so you can get your TA down a bit more AND so you can raise your pH while keeping your TA constant (by doing aeration instead of adding Borax). In other words, I don't think you should be adding any Borax at all and instead should just do the aeration at low pH (continuing to add acid until you get to your target TA) and then continue to aerate (stopping the addition of acid) to make the pH rise without affecting your TA.

Richard

[Simmons99]

Okay - I will when I get home - well - I'll just let the kids play that will aerate enough. Can tap water have high TA?

[chem geek]

Can tap water have high TA?

Yes it can. If your water is "hard", then it has high TA. Water hardness refers to the combination of both calcium and magnesium (and other minerals, but they are minor), but generally calcium is much larger in quantity than magnesium though this is dependent on the specific water source.

You can just test your tap water or you can look up the water hardness from your water utility district and then divide this number by 1.4 for a rough estimate of calcium hardness. The following table shows typical nomenclature for water hardness:

Soft 0-17.1 ppm 0-1 grains/gal
Slightly Hard 17.1-60 ppm 1-3.5 grains/gal
Moderately Hard 60-120 ppm 3.5-7.0 grains/gal
Hard 120-180 ppm 7.0-10.5 grains/gal
Very Hard 180+ ppm 10.5+ grains/gal

Some well waters can be well over 300 ppm in hardness. If the water source has passed through calcite rock (limestone), then it can pick up substantial calcium hardness since limestone is mostly calcium carbonate.

Richard