CH test reads 0?

[waterbear]

You win the prize!

I was careless, and didn't notice on my quick read through earlier. The '2-reagent' system combines the buffer and the indicator. But, on pools with lower pH, and relatively high alkalinity, there's not enough buffer in the indicator. That's why extra drops of indicator -- which add extra drops of buffer -- works, when the 'normal' number of drops don't.

(The pH of the sample has to be pretty high, for the indicator to work, and the 'buffer' tries to move the pH up high enough to work. But, pools with high alkalinity are resistant to pH change, thus the problem.)

Ben

So this could also explain my last test results. If the pH is not brough up high enough then the interfering magnesium would NOT precipitate out (or not completely) and the titration would show more of a total hardness reading instead of a true calcium hardness reading! (Current ALK at 110 ppm and pH at 7.4) When I did the experiements previously my pH was at 7.8-7.9, ALK 110. My ALK never seems to change much unless I really lower the pH and airate.

Bottom line, IMHO, is that the test in the Aquachem kit is not reliable for CH!