With your starting numbers, I calculate that you would have to add 67 ounces (about 8 and a third cups) of Muriatic Acid (31.45% hydrochloric acid) to get the pH down to 7.5 and that this would lower your TA to 188. I suspect that you will be fighting rising pH and should lower your TA, but your Calcium Hardness (CH) level is low and should be raised if you lower your TA.
If you decide to lower your TA level, then follow
this procedure, but also increase your CH to 300 and have your target pH (after lowering your TA) to be around 7.7. That should significantly slow down the tendency of the pH to rise. You could also add 50 ppm Borates for a further reduction, but should lower your TA first and see how that goes.
For the lowering of TA, I calculate it will take 108 ounces (13.4 cups) of Muriatic Acid to lower the pH to 7.0 and then with aeration and acid addition it will take a further amount of acid (added only when the pH rises to 7.2 to get to 7.0, then cycling) of 58.7 cups total in the aeration/acid cycle at which point the TA will be at 80 ppm. Then aeration alone will raise the pH to your 7.7 target. The process is essentially as follows:
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 )
