So just to be perfectly clear -- ONLY AERATION can be used as part of a procedure to lowering TA. There is NO BASE that should be used to raise pH when one wants to lower TA. You will simply swing back and forth in TA if you do that. You could accidentally lower the TA a little while the pH was low, but it would be due to aeration of some sort. The following is the TA lowering procedure I've posted elsewhere (and is based on Ben's original procedure
here).
ACTIVITY ..........
pH ....
TA ... (The following assumes 6.8 is the lowest measurement on the pH test kit)
==================
Acid .....................
- ........
- ... Add enough acid to bring pH down to 7.0
Aeration .............
+ .......
0 ... Aerate until pH rises to 7.2
Acid .....................
- ........
- ... Add enough acid to bring pH down from 7.2 to 7.0 (you may continue to aerate while you do this)
------------------------------------
Aeration & Acid ..
0 .......
- ... Continue this combination (cycling of the two above) until TA is at the target you want
then AFTER you have reached your target TA,
Aeration .............
+ .......
0 ... Aerate until the pH rises to your target pH (say, 7.5).
==================
Net of Above .......
0 ........
-
As for how much Borax it takes to raise or lower pH, the answer unfortunately depends on the TA level (and CYA level) and the starting and ending pH levels. The following are a few examples of what one pound of 20 Mule Team Borax will do in 10,000 gallons of water with a CYA level of 30 ppm:
at TA 80, will move pH from 7.00 to 7.11
at TA 80, will move pH from 7.20 to 7.36
at TA 80, will move pH from 7.40 to 7.63
at TA 80, will move pH from 7.60 to 7.89
at TA 80, will move pH from 7.80 to 8.11
at TA 120, will move pH from 7.00 to 7.07
at TA 120, will move pH from 7.20 to 7.31
at TA 120, will move pH from 7.40 to 7.55
at TA 120, will move pH from 7.60 to 7.80
at TA 120, will move pH from 7.80 to 8.03
So you can see that the same amount of Borax at higher TA makes the pH move less and that the same amount of Borax at higher pH makes the pH move more. Hope that helps.
Richard