The Sutro Monitor measures total alkalinity via a titration test similar to many liquid drop based test kits. During this test a color indicator is added to the water sample first and has very small amounts of acid added to it until a color change indicates the endpoint has been reached. The amount of acid added to the sample until the color change is equivalent to the amount of total alkalinity that was in the sample.
The amount of acid added to the sample each time correlates with the amount of total alkalinity consumed. For liquid drop based test kits, this is generally equal to 10 ppm CaCO3 for roughly 50 uL of acid. The Sutro Monitor uses nearly 1/20th of the amount of a liquid drop test, however, the volume of the sample is also reduced. This leaves the amount of acid the Sutro Monitor adds to the sample equivalent to about 25 ppm CaCO3*
The ranges displayed on the Sutro App directly correlate with the ranges that the monitor can measure based on the total alkalinity test. These ranges are shown in the total alkalinity table for reference.
Total Alkalinity Range Table
|Range||Total Alkalinity Range (ppm CaCO3)|
*The equivalent amount of total alkalinity varies between 20-30 ppm CaCO3 depending on the final amount of total alkalinity in the sample. This is due to some of the sample being lost when additional acid is added to the sample in the Sutro Monitor cartridge. High levels of chlorine may cause interferences with the monitor detecting the endpoint of the titration.