Just a thought here, but how does that work? If CO2 is so easily removed from the water by surface agitation, then wouldnt the process of putting into the test tube, and then shaking to mix, result in an errornous result?
Probably, plus the test assumes that the only buffer in the water is carbonate based, which may not be the case, a drop checker with a calibrated DKH solution is better anyway and is a continuous monitor.
