EC and PPM

Discussion in 'Hydroponics' started by piglet420, Feb 5, 2008.

  1. piglet420

    piglet420 Registered+

    I bought a EC/PH handheld meter from Hanna and I recalibrated it using the provided solutions. My ph was set correctly and using the EC solution it registered what the package said should be the correct number.

    I read this forum a lot and everyone always uses PPM when referring to the amount of nutrients they use. This causes me some concern because when I used my ppm scale on the meter in the test solution it didn't read near the 1500 ppm I assumed that it was going to read. HOWEVER it did read the right ph level and ec level in their respective solutions. So reading further through the manual that comes along with the meter it says that there is no calibration for PPM that calibrating it using the EC calibration method adjusts for the correct PPM. Hence my problem, if the EC is correctly calibrated then why doesn't it read the correct 1500ppm with the solution that I got.

    So I brought the meter back to my hydro store and he explained to me that was the way it worked and that I should be using EC to properly adjust my nutes.

    So that being the case can someone give me some insight on this and if it is the case is there a proper schedule of nutes per week that I should use in EC and not PPM?


  2. gainesvillegreen

    gainesvillegreen Registered+

    You will need to know the conversion rate of your meter (whether it's 0.5, 0.7, etc.). If you know this and you know the PPM or EC, you can concert PPM->EC and vice versa.

    Read the manual for your tester. It should tell you whether to use EC or TDS solution to calibrate your device. If it is EC as you suspect, you can calibrate it with an EC solution and still test your nutrients with a PPM readout.
  3. piglet420

    piglet420 Registered+

    I did calibrate it with EC solution and got the correct reading. So I want to make sure I understand this:

    Since I calibrated it using EC and it read the correct reading in the solution, then the PPMs are correct?

    If that is the case then why doesn't a known solution of 1500ppm read as 1500 ppm when calibrated correctly with EC solution? Or is the 1500PPM solution used to calibrate only PPM?

    An example would be since I calibrted with EC and got the correct reading. Wouldn't my PPM of a known PPM solution be 1500 instead of 1200PM?


  4. gainesvillegreen

    gainesvillegreen Registered+

    A TDS reading is a number derived from an EC test. The TDS is calculated based on a conversion factor, usually ranging from 0.5 to 0.7. If the EC reading is 1000 µS, the PPM reading will be 500 on a 0.5 conversion, and 700 on a 0.7. So for one solution with one EC reading, different TDS meters will read differently.

    You will need to find out if the conversion factor of your tester is the proper one for the nutrient schedule you intend to follow. If the schedule has EC readings, use those instead of TDS so you do not have to worry about conversions.
  5. Weedhound

    Weedhound Registered+

    If your's is reading something along the line of 1200....then it's a 0.5 conversion.
  6. piglet420

    piglet420 Registered+

    I just put together a new batch of nutrient and the PPM reading was 762 and the EC reading was 1525 with the water temp at 61C. Yes I know the water temp is cold, it's cold out in the garage (lol). With those readings, does that help me guess what I should be reporting or using as a feeding schedule? The Botanicare bottle says I need to cut the nutes down with RO water, or is that not an accurate reading? Should I be using the EC? I can't find an EC conversion scale for the nutes I'm using? Any suggestions?

  7. Weedhound

    Weedhound Registered+

    Do you possibly mean an e.c of 1.5?
    • Like Like x 1
  8. Illusion

    Illusion Registered+

    ec is double the number of ppm... i.e. 500ppm = 1 ec, 900ppm equals 1.8 ec.... ec... etc....
  9. piglet420

    piglet420 Registered+

    lol....I guess it's 1.5? I mean it says 1525 but maybe thats like saying 10 mm is 1 cm.
  10. Weedhound

    Weedhound Registered+

  11. piglet420

    piglet420 Registered+

    perfect! Thank you!

  12. Weedhound

    Weedhound Registered+

  13. gainesvillegreen

    gainesvillegreen Registered+

    A reading of 1525 is the same as 1.5, it's the units that vary. 1525 would be 1525 µS. You said it read 762 for TDS, which is half of the 1525, so your conversion factor is 0.5. This is also why it was reading 1200 PPM when you wanted 1500 PPM.

    I researched Botanicare to find what conversion factor they used for TDS and found nothing. I would e-mail them and just ask for the EC numbers or what conversion they used. You can also just use the recommended nutrients by volume.

    Weedhound is an experienced grower and uses Botanicare. There is a whole post on the Botanicare regimen.
  14. piglet420

    piglet420 Registered+

    Thanks folks so much! I'll be doing all the reading tonight and get it squared away. Not sure how to give rep points or props. If you show me where it is in the forum I'll make sure to give some to you both.

    Thanks again!

  15. gainesvillegreen

    gainesvillegreen Registered+

    All you have to do is click the little blue scale icon on the top of an individual post. If you hover your mouse over it, it will say 'Add to Nickname's Reputation'.
  16. piglet420

    piglet420 Registered+

    I just wanted to let you know that I replaced my res. I'm going to start measuring using EC because I keep getting told that's the best way to measure the res content. Additionally, I have a scale that converts the EC with the manufacturer of my meter.

    With that said my EC is now .670 which measures between 300 and 350 PPM (roughly 325). My ph has been constant at 6.0 for the past 2 days but I'm going to bring it down a little just for arguements sake cause it seems most people like 5.8.

    My leaves on that one plant still seem turned up, no discoloration on the leaves. They look like "canoes" is the best desription I can give. A book that I have mentions magnesium defeciency, but I am no authority on this.

    I'm going to give it a few more days and then change the res again.

    Today is day 13 of veg.
    EC is .670
    PH 6.9
    Temp 75
    Bot Pro grow and Liquid Karma
    Light is MH 400w about 20inches from canopy and running a fan

    Last edited: Feb 10, 2008
  17. herbie the love bud

    herbie the love bud Registered+

    Generally the already affected leaves won't repair, but it might stop from getting worse and new ones won't develop that syndrome. So don't try driving by the appearance of those plants. Just let time and your new solution do its thing. Don't change water for another week.
  18. piglet420

    piglet420 Registered+

    Will do and that's the general feeling I had as well.


  19. piglet420

    piglet420 Registered+

    Well today is the 5th day of the new res. Something I have noticed over the past 2 days is that the color of the liquid has turned from that "nutrient brown" to almost clear. Obviously the bottom of the res has some of the coloring from the settlement of the nutrients but I stir 2 times a day to make sure I keep everythng moving about. I also have 2 large round air stones on all the time in the res to make sure there is circulation and more oxygen. The other thing I have noticed is that they are using more res solution and I had to adjust my PH 2 times yesterday and once this morning. I guess my question is, is this normal? Is this how I know they are using the nutes and is it a good indication that I need to add more solution to the res. I'm still keeping it at about .67 EC as everyone previously suggested and they are getting really bushy now.


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