There are several companies selling other Hanna instruments they indicate will test Colloidal Silver but were really designed to measure TDS (total dissolved solids). As calibrated from the factory the TDS meters will normally read only about one half the PPM of ionic silver that the PWT meter will read. Most of the Hanna TDS instruments have ranges of 0-999 PPM or 0-1999 with 2% accuracy of full scale. That means the unit can be off by as much as 20 or 40 PPM at the low OR high end of the range or at any reading. If you are trying to measure Colloidal Silver at the 5-15 PPM range, it is obvious that a 20 or 40 PPM possible error is not acceptable especially if the reading is only half the actual amount of silver in the water. The PWT will not be off more than 2 PPM so you can see how much more accurate it is.

The PWT meter is the only meter that works at the accuracy and range desired to measure CS.


http://www.silvergen.com/ppm_meter.htm

It should be ok as they recommend it for ionic silver. It has a larger scale of 0-999 ppm so it might not be the most accurate but it will give you a good reference point. Keep in mind that total dissolve solids is a little different than just silver.

My Hanna meter measures conductivity instead of PPM and is on a scale of 0- 100 uS. You have to use a formula to get ppm of silver. If I try to measure my tap water it goes off the scale.