Tds Meters With Different Reading

[Avinitlarge]

I have just bought a DM1 in line monitor and I already have a TDS 3 handheld. I have calibrated both of them to 240ppm but when I check the TDS of my tap water I get 2 different readings. The handheld reads 215ppm and the inline reads 175ppm. Can anyone suggest anything??

 

[jm_]

I have just bought a DM1 in line monitor and I already have a TDS 3 handheld. I have calibrated both of them to 240ppm but when I check the TDS of my tap water I get 2 different readings. The handheld reads 215ppm and the inline reads 175ppm. Can anyone suggest anything??

Clearly some things out,, you are reading the in-line AFTER the water flow, then your testing at the same point,,,

Zero with solution is best or if you know friendly LFS they can test RO for you and you can cross check and see - they should be the same or extremely close, when TSDs are taken if you move the pen the reading changes so steady hand
You not testing in a polluted pop are you (just an idea)