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TDS .5 vs .7 conversion factor?

Discussion in 'Nutrients' started by FootClan, Dec 12, 2010.


    FootClan Well-Known Member

    on the back it says " EC start 1.2 end 2.0 ?

    NLXSK1 Well-Known Member

    Well, there you go. Although I would use 1/2 of the recommendation to start.

    FootClan Well-Known Member

    so is saying that the highest concentration of nutes i should have in my reservor is 2.0 on a EC meter?? is that what its saying ?

    2.0 EC is a 1000ppm but i thought iwanted to be around 1400 ppm at the plants peak?? so wouldnt i be going over that ...Im already at 1130ppm so isnt that already over 2.0 EC once again even more confused now......

    I think ill just go back to not carrying and just follow the feed chart like im already doing........I mean my plants look great i have no problems i just wanted to understand this more but it seems more hassle then helpful.......

    NLXSK1 Well-Known Member

    Again, PPM is not consistent across the board. 2.0 EC is 1000 PPM if the conversion is .5 but if the conversion is .7 then it is 1400 PPM. It depends on the meter.

    Stick to EC.

    FootClan Well-Known Member

    well my conversion is .5 so that means 2.0 ec would be 1000ppm but im already over that and the Humboltwhole sales protect support guy said i can be as high as 1400 ppm at peak feeding......so i guess the "start 1.2 end 2.0 EC is NOT correct on the back of the bottle.....

    Stonefree69 Member

    It's all relative. Get an EC meter and read that each time you do a weekly res change or top off. If the reading is down between res changes/top offs it means your plant could use more nutes. If the reading is higher, then you should use less nutes. If the reading remains the same then you're on target. Just listen to what your plants tell you. Obviously your plants will use more nutes as they grow from week to week, and the changing EC will reflect that.

    If your EC meter is consistent in readings your plants should be perfectly fine. My favorite meter is the Bluelab Truncheon, which doesn't need calibration (from straying in it's readings) and is very accurate as well as a fav among many growers.

    thinn Active Member

    I do not have a ppm meter from hanna or eutech so I am guessing that they only read in their specified scale (hanna @ 500). I think the problem arises with the meter we both chose, the bluelab truncheon, because it has conversion for both on it. Essentially leaving it up to you to decide which to go off of. I have been reading mine on the 700 scale and pretty much adjusting down as my plants react to it. I would think if you want a more definitive answer, you would have to ask someone who treats pool water. I believe alot of those chemical bottles tell you what to read your ppm at. Just my 2 pennies..

    mundaiis Active Member

    I read through the first bit, it seems if you are confused it is because there is a grand over complication going on right here.

    There is EC (Electric Conductivity), CF (Conversion Factor), 500, and 700 or you can say .5, and .7.

    EC is a multiplication of 1.
    So to get EC, you times your EC reading by 1.

    CF is a multpilication of 10.
    So to get your CF reading from a 1.0 EC,
    1 x 10 = 10, Therfore CF = 10.

    .5 is a multiplication of 500, therefore 1.0 EC will be 500ppm.

    .7 is a multiplication of EC by 700, therefore 1.0 EC will be 700ppm.

    hexthat Well-Known Member

    I go by EC, my ppm stick has EC tds 0.5 tds 0.7.

    I have had a purple kush in flood to drain 6 inch rockwool cube love 2.7 EC of nutrients and it vegged very well was a wonderful 3 foot mother. I say root-bound is lack of nutrients. The tips are all that burned every once and a while I'm guessing from too much nitrogen seeing how it was only using GH series and its hard to get perfect spectrum with GH.

    jonro Well-Known Member

    But see, if you go and use the General Hydroponics feeding chart for example, it is using PPM. along with a lot of other charts, how do people know what conversion rate of ppm the chart is using?

    beuffer420 Well-Known Member

    Call general hydro and ask them. and then whatever meter your using see what they call for to dial the meter into desired scale.

    elsheepo New Member

    To the OP: The different conversion factors were developed to measure different salts. Some conversion factors are better suited for measuring certain solutions. I have put together this PDF for you, it breaks down TDS and EC. Again, to clear up any confusion, each reading by your meter, as far as ppm's are concerned, is correct, in it's own respect, because each conversion factor was designed to measure specific, and different salts. The one to choose, is whichever one your nutrient supplier uses to measure their products. I can speak for Fox Farm, they use 0.7 aka: TDS 442

    Attached Files:

    Last edited: Oct 20, 2016

    jsquared89 Member

    Using EC to measure TDS is not the best way to do things. It's good when you want to compare similar feeding solutions in terms of keeping things in spec, but other than that, it's not a great measurement.

    If you are truly concerned about the exact TDS in your feeding solution, send a sample of it to a water testing lab for an "Irrigation Suitability Assay". It will cost you $35-60 depending on where you are and who you go with. Take that number you get and work with it instead of any 500 or 700 scale.
    Marcel Rehel

    Marcel Rehel New Member

    Hi, I'm not an expert nor providing a response to soil quality for plants. From what I've read and understood from various posts, the 0.5 conversion factor from EC to TDS can be used to estimate salt (NaCl) content in water (ex. in salt water pools) in order to decide whether to add salt to your pool to achieve a proper chlorination level. The 0.7 conversion factor can be used to estimate overall dissolved solid levels in natural water (ex. well water) in order to adjust your water softener settings so you don't waste salt between regenerations. That's my understanding at least from a practical level and I hope it helps you. The thing to remember is that a EC/PPM meter measures EC (i.e. electrical conductivity) acurately but TDS levels depends on the types of solids desolved in the water being tested (ex. salt + calcium + iron + etc.). I bought a EC/TDS meter which allows for both 0.5 and 0.7 conversion from EC to TDS and I absolutely love it.
    Last edited: Jul 19, 2017

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