PPM .5 or PPM .7 (4-4-2) EC µ or mS Which one to use?

[buzz62]

My new TDS/EC meter has two settings for ec (µ or mS), and either ppm.5 or ppm.7. The ppm.7 reading reads a lot higher, ppm.5 =1000 ppm tds vs ppm.7=1350 ppm tds in my Advanced Nutrient solution at the 4 ml/L rate. It's EC is 1.9 mS. I had read somewhere that AN uses ppm .7 for their baseline, but this scale is totally new to me. Should one assume that most of the ppm readings one sees on this site are in the lower reading ppm.5, which is what my first ppm pen is in? Reading Ed Rosenthals handbook it appears he is using the .5 ppm scale as he states "to be wary of nutrient solutions stronger than 1200 ppm or EC 2.4 mS", and he does discuss the ppm.7 a little, but does not reference which one he is using elsewhere! I gotta say, seeing the higher reading scares the heck out of me!!

 

[Alienpus]

To avoid all the confusion we should all use EC mS and do the math for uS and PPm

Most pens display in microsiemens (uS) some in millisiemens (mS) mS = uS / 1000

PPM is calculated from microsiemens by multiplying by .5 or .7 PPM = uS x .5

so a pen that displays 1200 is displaying in microsiemens divide by 1000 gives 1.2 EC. Take the 1200 multiply by .5 and you get 600 PPM or multiply by .7 and get 840 PPM

 

[buzz62]

To avoid all the confusion we should all use EC mS and do the math for uS and PPm

Most pens display in microsiemens (uS) some in millisiemens (mS) mS = uS / 1000

PPM is calculated from microsiemens by multiplying by .5 or .7 PPM = uS x .5

so a pen that displays 1200 is displaying in microsiemens divide by 1000 gives 1.2 EC. Take the 1200 multiply by .5 and you get 600 PPM or multiply by .7 and get 840 PPM

Thanks! I agree, one way to do it would be great! Millisiemens it is! So now that I have a pen that can measure that, is 2.4mS or 1200 @.5ppm an upper limit as Ed says?

I just made a batch of AN Sensi Grow at the label rate of 4ML /L and added AN Big Bud at the recommended 2mL /L. I get an EC reading of 2.1mS and 1050@.5ppm and 1482 @ .7ppm with my pen. And your math pretty much confirms this, so thanks for clearing that up with an excellant explanation.