Originally Posted by Spartan1979
Per the reports, total Alkalinity is 53 ppm
Then, theoretically, it should only take 3 mL of 50% acid. But there are lots of reasons why the actual alkalinity you are encountering is probably not the number in the report which is most likely an average. And your measurement of pH, your measurement of the amount of acid and even the strength of the acid may not be spot on.
If you really want to know what the alkalinity of the water is you would put your pH meter into it and precisely add acid of precisely known strength to it until the pH reached 4.3. It's pretty clear that you are essentially doing just that but not being so precise. What I'm getting at is that 5 mL vs 3 mL with the latter based on a municipal water report isn't, IMO, that much of a discrepancy.