- effects of adding acid shows how much TA is lowered and approximate PH. but the TA tab just says lower PH with acid and aerate . Should there be a suggestion in that window with how much acid to use? or was there a worry people wouldn't do it right (only lower to 7.0-7.2 for each addition? )
I assume you mean it says on the TA tab "To lower TA you reduce pH to 7.0-7.2 and then aerate to increase pH"?
Firstly, note that like it says on effects of adding acid, pH is approximate cause it's assuming a TA around 100 or so. If you pull open the pH tab, the amount of acid to lower pH to a target value uses your actual TA value in the calculation for volume of acid to add. So the effects of adding tab, pH changes are approximate, but on the pH tab, the amount of acid is pretty darn close assuming you have entered the current TA of the pool (and borates, if you use them).
On your second note, the reason it doesn't list an amount of acid to use is because adding too much acid will tank the pH, which will damage any metal in the pool (pump shafts, heaters, SWCG, etc). To avoid going too low, the acid used to lower the TA must therefore be added incrementally and then the pH brought back up by aeration before more acid is added. That's why it says to lower the pH to 7.0-7.2 then aerate to increase the pH, to avoid people taking the pH down below 7.
Note that if desired, you can use the pH tab to calculate how much acid to add to drop to 7.0 based on current TA/borates. Then if you plug this number into effects of adding you'll see how much the TA will drop. But again, do not ever just add acid to target a specific TA from your current TA.
If anything, it may be useful to have a section (perhaps toggled on as a setting only if users desire) within the pH tab itself that shows the TA drop adding the acid will give?