[dave f]

ive got 2 identicle tds meters ,i tested my tap water with each one was 123ppm and the other was 99ppm so i tested the water in my tank both readings were 000ppm ???strange

[Tom White]

The calibration of the TDS meters will be slightly different, however, the TDS meter works by transmitting an electrical current in the water.  Electricity cannot pass through purified water - only through water with dissolved solids in it.

So your TDS 000 is to be trusted.  If your pure water had solids in it; even a tiny amount; you would get two different readings on your TDS meter such as (for example) TDS 10 and TDS 23.

I wouldn't worry at all, if I were you.

[dave f]

exelent reply cheers

[bumper]

i calibrated  mine in some calibrated solution now they both read the same i put both in tap water and they read the same.