How much borax to raise PH?

[chem geek]

Just to be technically correct, aerating raises the pH with no change in alkalinity. Adding acid lowers both pH and alkalinity. So the combination of the two ends up lowering alkalinity at a given pH. Carl explained this in this thread.

ACTIVITY .......... pH .... TA ... In your case (assuming 6.8 is the lowest measurement on the pH test kit)
==================

Acid ................. - ........ - ... Add enough acid to bring pH down to 7.0 (you were already below that so you skip this step)

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 ........ -

So as the other posters said, when you are starting out with low pH but also have high TA, the best thing to do is to just aerate as that will raise the pH without raising alkalinity and gets you started in the above procedure that lowers alkalinity. So specifically in your case, assuming that 6.8 was the lowest measurement on your pH kit, you should have started aerating until you saw the pH rise to 7.0 and then keep aerating to let it rise to 7.2 and THEN add acid to bring it back down to 7.0 (after that, you bounce between 7.0 and 7.2 through aeration and acid addition -- all the while your TA drops). You never target the lowest pH measurement (6.8 on your kit) because you can never really know if it's truly at that pH or if it's lower. Hope that helps.

Richard