Going to try a sort out temperature first and then look at pH.You will still have to compensate for starting pH otherwise you could easily find yourself with an additional swing of 0.3dkh depending on time of day your sample is taken.
I'm finding starting pH very confusing. The most surprising part is how long it takes to return to normal after the test, > 2 hours, not stirred.
So at 1/2 hour test intervals the starting pH is only about 7.1.
When I get a chance I will have a look at this.Try measuring the volume required to shift the sample from 7.8pH to 4.4pH
You need to ignore the first acid input until the sample is below 7.8pH