(I wrote this at the same time as Jason. We both refer to the same paper discrediting this method.)
The "slug" or "acid column" method was fully discredited
here. You lower pH by adding acid slowly over a return flow with the pump running. The TA is somewhat lowered at the same time as pH and TA move together.
To lower the TA by itself, one must use a combination of acid addition with aeration and the procedure is outlined as follows (I don't think we have a sticky for this yet).
PROCEDURE ..........
pH ..
TA
===================
Acid .......................
- .....
- ... Lower pH to 7.0 ( or next to lowest measurement on pH test kit, but not below 6.8 )
Aeration ................
+ .....
0 ... Waterfalls, fountains, showers, point returns up, splash, run SWG
Acid .......................
- .....
- ... When pH from aeration rises to 7.2, add acid to lower to 7.0
-----------------------------------
Aeration + Acid ......
0 .....
- ... Repeat the above until the TA gets to your target ( e.g. 80 ppm )
Aeration ................
+ .....
0 ... Aerate (and no longer add acid) until pH rises to target pH ( e.g. 7.7 )
===================
Net Result ..............
0 .....
- ... Net result is lowering TA with no change in pH ( unless final pH target is different than starting pH )
In the procedure above, I describe adding acid when the pH hits 7.2 but you can do it whenever you want such as waiting for the pH to go higher. It's just faster to keep the pH lower during aeration as this outgasses carbon dioxide more quickly.
Richard