TDS meters should only be used as point-of-reference devices.

They are merely cheap electrical conductivity (EC) meters that have a
built-in conversion factor for solids. Unfortunately, the conversion factor
should change with the specific ions in the solution to be measured, making
the built-in one worthless for "real" data. Read this:
http://www.firstrays.com/tds_and_ec.htm

--

Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies. Books, Artwork, and lots of Free Info!


"Gene Schurg" wrote in message
...
Recently, I visited a hydroponic supply brick and mortar store to look
at TDS meters. They had some from the low end to $150+. Some needed
calibration (the cheaper ones) and some of the more expensive ones were
self calibrating.

What are others using and would you recommend it to another grower?

Good Growing,
Gene