The actual amount of Muriatic Acid you need to add to get a desired change in pH is dependent on the starting and ending pH as well as the TA level. The formula given in the previous post works correctly going from 7.7 to 7.5 with a TA of 110. Therefore, the advice of adding less than the calculated amount and seeing the effect before adding more is good.

If I can figure out how to simplify the formulas that account for starting/ending pH and current TA, I'll update Michael Smith (the creator of BleachCalc) with some new formulas that will be more general. I have a spreadsheet that calculates all this stuff, but it is way too complicated for general use (though I'm working on simplifying it).

Richard