The reported tolerance of the Aquacheck strips is usually about +/-400ppm. However, they are affected by humidity and the people neglect to read the instructions where they specifically say that the strip must be placed in a test tube filled with about 1" of water. And every bottle of strips is different because the number on the strip is calibrated to a chart on the bottle.
The K-1766 drop based titration test uses a 10mL water sample volume and has a tolerance of +/-200ppm (the titrant precision is 200ppm/drop). However, one can simply use a larger water sample and get better precision - a 25mL water sample will have a titrant precision of 80ppm/drop. Also, the K-1766 measures the EXACT chloride ion (Cl-) concentration and has no interferences associated with it (unless you add cyanide or bromine to your pool water). So the salt level determination from a K-1766 is a very accurate representation of the salinity level of your water.
