pH Adjustment Discrepancy

[cwswifty]

My pH had drifted to 8.0 and I wanted to add MA to bring it down to 7.8. The pH adjustment screen, which has you enter your TA (mine was 60), calculated that I needed to add 7.9 oz of MA to reach my target (7.8). I added that, rechecked in 20 mins and was still above my target. Out of curiosity I went to the Effects of Adding section with 7.9 oz of MA to my pool and it showed the pH being lowered by .1 (7.9 in my case). I added another 7.9 (8 let’s be real) oz of MA and 20 mins later I was at 7.8. I would have thought that the pH adjustment screen which includes your actual TA would have been the most accurate way to determine MA demand. What I described suggests maybe not. Thoughts?

 

[Newdude]

1) effects of adding doesn't ask your TA
2) read the disclaimer at the bottom of effects of adding
3) an 8+ looks like an 8. It could be a 9. The same for being low as it only reads to 6.8. If it's really a 6.2 it will take a couple adds from 6.8 to your target, to be back in the 7s.

 

[cwswifty]

1) effects of adding doesn't ask your TA
2) read the disclaimer at the bottom of effects of adding
3) an 8+ looks like an 8. It could be a 9. The same for being low as it only reads to 6.8. If it's really a 6.2 it will take a couple adds from 6.8 to your target, to be back in the 7s.

1) I know.
2) I did.

It surprises me the the 2 screens differed by 100% and the one that did not account for actual TA appeared to give the correct answer.