TDS Tester - STPP

[DADoES]

 
Question for anyone who is knowledgeable in chemistry and lab:   Would a device such as this be usable to determine proper dosing of STPP? What would be the procedure, the reading or change in reading, to be targeted?

http://www.filtersfast.com/HM-TDS-3-Meter-For-Filter-Apps.asp

 

[sudsmaster]

Since phosphate would be considered a dissolved solid by the meter, one probably couldn't use the meter directly to determine optimal dosage.

However, one might check the final rinse water for TDS and see how varying amounts of STPP in the wash water affect final TDS in the last rinse.

To complicate matters, hard water generally has high TDS. Not sure what effect STPP would have on TDS readings of hard water. I suspect no effect, or an increase in TDS equivalent to the amount of STPP added to the hard water.