That's good, I got it on ebay since they are usually the cheapest. it said 0-1999 ppm. I don't understand how that related to what you said about .2 being good and over .6 being too much TDS.
Interesting you've just asked a similar question to someone else on that other thread! I'll try and post a reply to the other question tonight and a formula for converting NPK ratios into ppm and EC, which may help.
There is a chart floating about that converts ppm to EC, TDS and ppm values, unfortunately I don't have it in scan form - only in book form. Someone in the Hydro section may have a scan of it. Just to complicate matters, each EC manufacturer has its own ppm values!
From my book -
EC = Hanna, Eutech, Truncheon
0.1 EC = 50ppm, 64ppm 70ppm
0.2 EC = 100ppm, 128ppm 140ppm
0.3 EC = 150ppm, 192ppm 210ppm
0.4 EC = 200ppm, 256ppm 280ppm
0.5 EC = 250ppm, 320ppm 350ppm
0.6 EC = 300ppm, 384ppm 420ppm
0.7 EC = 350ppm, 448ppm 490ppm
0.8 EC = 400ppm, 512ppm 560ppm
0.9 EC = 450ppm, 576ppm 630ppm
1.0 EC = 500ppm, 640ppm 700ppm
You can pretty much calculate all the other higher values from this chart (eg 1.1 EC would be 550ppm on the Hanna scale).
So by using the chart, let's assume you use a Hanna EC meter, 0.2 EC would be 100ppm and 0.6 EC would be 300ppm. So what I was saying in regards to the TDS of the irrigation water, if it has a ppm of 100 or less on the Hanna scale, then it should be fine as it is, if it's over 100ppm, then you might want to think about mixing it with distilled or RO water (which has an EC of 0, or should do, depends on how many stages your RO machine has) to enable you to use sufficent quantities of nutrient in your solution without raising the overall EC or ppm to too high a level.