Okay, I had some rockwool leftover from my Emily's Garden and I used it to replace the aerogarden sponges. I cut to fit the re-used pods from my herb growing in the aero garden. I soaked it for 24 hours in 6.0 PH water. I then placed 4 tomato seeds in the rockwool and covered with rockwool, then the pod covers. The seed packet says 8-10 days for germination. It has been 11 days and no sign of germination. I am using Ultragrow nutrients mixed per the label for seedlings. The light has been on for 8 hours a day. Suggestions??
I use EC myself as well. Just by coincidence I came across this meter recently and remembered it is x500. It's unfortunate that 'affordable' meters for new growers normally only give ppm values.
If I'd taken the time to find the manual (thanks bab43), then the meter does indeed look to read the x500 scale, in fact, Hanna in the USA uses the x500 scale so this seems to be correct.
Confusion abounds; you see the problem now. Different countries and different manufacturers use different PPM's, you will also find the x640 scale! When someone talks about PPM in forums, you have no idea what scale they are using (x500, x640 or x700), this makes things difficult.
Consider this: the same solution can read different PPM values with different PPM meters! The EC will always be the same though across all meters.
That's why I have always said to use EC, simple, EC is EC.
Peat is right about wanting to double-check your meter - I'm quite certain that the HM meters are on the x500 scale.
The meter at the manufacturer's site: www.tdsmeter.com/products/tds4.html
The manufacturer's calibration information: www.tdsmeter.com/products/calibrationsolution.html
If I look at "Solution Conversions" on the second link and divide 342 by 500 as Peat suggests, it comes out to EC 0.684 mS or 684 µS, so close to the 700 µS on the manufacturer's site. If you divide by 700 it doesn't even come close.
You should wait for Peat's confirmation though. If I'm wrong then I get to learn something as well.
You're right, Peat. It is x700. Now I can better use your great resource!
If you do learn more about the 500 or 700 conversions, that would be cool.
By the look of things your meter uses a 342 ppm NaCl calibration solution, I'm fairly sure that you are using the x700 conversion (as opposed to the x500).
Have a look at my guide, Part 2 Page 6 - this will give you a good idea of the EC range. For a highly accurate reading, divide you PPM by 700 to obtain the EC.
I'd need to check on this further though, if your are using the x500 then divide the PPM by 500 to get the EC.
To convert from EC to PPM, either multiply by 700 or 500.
PPM is a pain as there are too many standards, EC is simple, one reading which is universal and understood by all.
FABULOUS RESOURCE, PEAT!
I do have one request, though. I use this meter http://www.amazon.com/HM-Digital-Pocket-TDS-4-Quality/dp/B0002T6L5M/ref=...
It gives straight ppm, so I don't understand your TDS X readings. Is there a way to convert EC to straight ppm?
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