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How To Determine Your Plants Preferred Nutrient Strength

Discussion in 'Hydroponic Growing' started by GoldGrower, Mar 27, 2013.

  1. #1 GoldGrower, Mar 27, 2013
    Last edited by a moderator: Jun 16, 2014
    A lot of people seem to struggle with how much to feed their plants so I have made this thread explaining my method of keeping the reservoir 's nutrient strength the same as what the plants are currently taking up.

    Plants take up nutes and water at their own prefered strength. To make it as easy as possible for them to do this, therefore making the process as fast as it can be, I match my reservoir's nutrient strength to it.

    To do this you will need a nutrient strength meter, be it a CF, TDS, PPM, EC or any other, they do the same job.

    First of all make up some nutrient solution, go with a weak one to start with to make sure you don't kill the plants. For 1-3 week old plants try at an EC of 0.30, for grown on plants maybe 0.50. Under a week I give them just water.

    Write down the exact EC/ppm figure.

    24 hours later test it again.

    If the EC has risen, then it means the plant is taking up a solution that is weaker than what you have in the reservoir. So add more water to lower it down to a little lower than what you had it 24 hours ago.

    If the EC has fallen, then it means the plant is taking up a solution that is stronger than what you have in the reservoir. So add more nutes to raise it up to a little higher than what you had it 24 hours ago.

    If there has been no change in nutrient strength but you can see the plant has used up some of the solution you know you have the strength exactly the same as the plant is taking it up.

    As the plant grows it requires stronger and stronger solution until it reaches a plateau. This plateau will be different depending on set up and even individual plants. Mine usually plateaus at around 1.20 to 1.30. After this you won't have to worry about checking so often as it shouldn't move much even when the water level drops down

    Adjust your PH regularly, try to not let it go out of 5.5-6.5 range for more than a few days.

    As a side note I strongly recommend using a single bottle nutrient as it makes it so much easier than mixing your own recipes. I have been using growth technology's ionic grow and bloom and they are superb. You just use the grow bottle for vegging and the bloom bottle for flowering. There's no mixing involved like a+b nutes

    Here's table to help you convert your figures

    When it comes to refreshing the whole reservoir my current theory is once the plant has taken up a volume of water that is equivalent to 4 times the volume of the reservoir then it's time to empty it out and refresh with a new solution. This is a safe guard in case your chosen nutrient does not contain the exact same ratio of elements that the plant is taking up. You could change it after the plant has taken up 3 times the volume if you want to play it safe 
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  2. Good, straight forward and clear. Thanks
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  3. Total Dissolved Solids (TDS) is the best measurement of the nutrient concentration of a hydroponic solution. To estimate TDS, one can use a meter that measures the Electric Conductivity (EC) of a solution, and convert the number to TDS in parts per million (ppm). Many meters will do this conversion.

    Total dissolved solids (TDS) is typically expressed in parts per million (ppm). It is a measurement of mass and determined by weighing, called a gravimetric analysis. A solution of nutrients dissolved in water at a strength of 700 ppm means that there are 700 milligrams if dissolved solids present for every liter of water. To accurately calculate total dissolved solids (TDS), one would evaporate a measured filtered sample to dryness, and weigh the residue. This type of measurement requires accurate liquid measurement, glassware, a drying oven, and a milligram balance. Example: 50 mL of the 700ppm solution would leave 35 mg of salt at the bottom of a crucible after drying.

    Electrical Conductivity (EC) is expressed in siemens per centimeter (s/cm) or milliseimens per centimeter(ms/cm). It can be determined with an inexpensive hand held meter. Nutrient ions have an electrical charge, a whole number, usually a positive or negative 1, 2, or 3. EC is a measurement of all those charges in the solution that conduct electricity. The greater the quantity of nutrient ions in a solution, the more electricity that will be conducted by that solution. A material has a conductance of one siemens if one ampere of electric current can pass through it per volt of electric potential. It is the reciprocal of the ohm, the standard unit of electrical resistance. A siemens is also called a mho (ohm backwards).

    For convenience, EC measurements often are converted to TDS units (ppm) by the meter.

    The meter cannot directly measure TDS as described above, and instead uses a linear conversion factor to calculate it. Everyone’s nutrient mix is different, so no factor will be exact. The meter uses an approximate conversion factor, because the exact composition of the mix is not known. Conversion factors range from .50 to .72, *depending on the meter manufacturer, which do a good job of approximating a TDS calculation from the meter’s measurement of EC.

    * All ppm pens actually measure the value based on EC and then convert the EC value to display the ppm value, having different conversion factors between differing manufacturers is why we have this problem communicating nutrient measurments between one another.

    EC is measured in millisiemens per centimeter (ms/cm) or microsiemens per centimeter (us/cm).

    One millisiemen = 1000 microsiemens.

    EC and CF (Conductivity Factor) are easily converted between each other.
    1 ms/cm = 10 CF

    "The communication problem"...
    So again, the problem is that different ppm pen manufacturers use different conversion factors to calculate the ppm they display. All ppm (TDS, Total Dissolved Solids) pens actually measure in EC or CF and run a conversion program to display the reading in ppm's.

    There are three conversion factors which various manufacturers use for displaying ppm's...

    USA 1 ms/cm (EC 1.0 or CF 10) = 500 ppm
    European 1 ms/cm (EC 1.0 or CF 10) = 640 ppm
    Australian 1 ms/cm (EC 1.0 or CF 10) = 700 ppm

    For example,

    Hanna, Milwaukee 1 ms/cm (EC 1.0 or CF 10) = 500 ppm
    Eutech 1 ms/cm (EC 1.0 or CF 10) = 640 ppm
    Truncheon 1 ms/cm (EC 1.0 or CF 10) = 700 ppm

    Calculating the conversion factor

    If your meter allows you to switch between EC and TDS units, your conversion factor can be easily determined by dividing one by the other.

    Place the probe in the solution and read TDS in ppm. Change to EC on the meter and read EC in ms/cm.

    Conversion factor = ppm / ec.

    [Note: ms must be converted to us: One millisiemen = 1000 microsiemens (1.0 ms/cm = 1000.0 us/cm)

    According to the chart below:
    1.0 ms/cm = 500 ppm (USA Hanna)
    1000 us/cm = 500 ppm

    Conversion factor = ppm / (ms/cm * 1000)
    .50 = 500ppm / (1000us/cm) ]

    The answer is your meter's convertion factor and should be a number between 0.50 and 0.72 To improve accuracy, take ec and ppm readings from your res daily for about ten days. Average the conversion factors. The more data points that you use, the closer you will be to finding your true conversion factor.

    When reporting your PPM in a thread, please give the conversion factor your meter uses. For example: 550 PPM @0.7 or give the reading in EC, which should be the same meter to meter.

    It may also be advisable to give the starting value of your water; there is a huge difference between RO and distilled water with a PPM of approximately 0 and hard tap water of PPM 300 @.5 (notice the conversion factor so others can work out the EC) or well water with a conductance of 2.1 ms/cm.

    A note to Organic Growers:
    An EC meter has fewer applications for a soil grower because many organic nutrients are not electrically charged or are inert. Things like Superthrive or Fish Emulsion, blood meal, rock phosphate or green sand cannot be measured with a meter reliably when they are applied or in runoff. Meters can only measure electrically charged salts in solution.
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  4. Good stuff you two.
  5. Thanks GoldGrower, good to know!
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  6. this is a great post and super useful.
    I guess that this could be modified for coco. check the ppm of nutrient solution. feed. wait one day. check ppm/ph of water. saturate bucket and check runoff.
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  7. Very helpful and easy to understand thanks for the insight
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  8. Question. I use a separate reservoir for my grow and I was wondering, if I can adjust the PH and PPM in the reservoir itself do I have to dump the water weekly? I use a recovery system which recycles the water. If i understand correctly, the PPMs don't give a specific nutrient count so if I keep adding without dumping I might create higher levels of a certain nute and ill be risking lockout?

  9. first PPM is a measurement of TDS. What you mean is youll be raising your TDS. think of it like "I need ot increase my distance by X feet" not "I need to increas my feet" :)

    second, a complete res change is needed for the proper balance of nutrients in solution. Each strain can be a little different as to how much of each nute they need so the levels get messed up so complete res change is best as each formula is a bit different anyway.

    you can asjust things in the res with caution
  10. Ah, I get it now. Thanks for the reply. I was thinking I could get away with not changing the reservoir but now I see why that's a bad idea. This is why I joined up here.
  11. #11 GoldGrower, Mar 31, 2013
    Last edited by a moderator: Apr 30, 2014
    yes but this is only really a concern if your res is very small and/or your chosen nute range is not very well suited to the plants you are using them on.
  12. #12 ELRooster, Apr 16, 2013
    Last edited by a moderator: Apr 16, 2013
    GoldGrower I have a question in regards to checking after 24hrs, If my plants use 5-7 gallons of water wont my concentrations/reading go up no matter what? It always seems that when I try this method that my plants use so much water that my readings always rise even when using a light nutrient solution. Also you mention not to top off with any nutrients, if you flush and check the next day can you add water and nutrient if they need them or is it better to flush again? Lets say my first reading was ms/cm 1.44 PH 5.8 and PPM of 1050. If the next day my readings are ms/cm 1.21 PH 5.9 PPM 879 Would it still be ok to add water and Nutes or do I need to flush and do the whole process over again. Thanks
  13. #13 GoldGrower, Apr 17, 2013
    Last edited by a moderator: Apr 30, 2014
    5-7 gallons in 24 hours? They would have to be huge plants. That is an extreme number, what size is your nutrient tank? Normally the answer is no, because if your plants were using up the nutrients in a higher concentration than what the nutrient solution is, then the strength would drop

    if it's rising then your plants are using more water than nutrients, the idea is to have the nutrient solution in the exact same balance as what is in the plant

    what do you mean when you say "flush"? Flushing is for soil. In hydro you just empty the solution and its gone. You then replace it with the correct strength, is that what you mean when you say flush? I don't really understand what your asking if I'm honest

    If the ppm has dropped I would simply add a dash of nutes to bring the figure back up to a little higher than it was before
  14. I drain and fill my reservoir every 7 days. But I have always ran very high nute levels. So when I drain and fill I adjust my PH and run/flush my system for 24hrs (This is what I ment by flush). Then add fresh nutes. I'm kinda old and these forums are new to me so it has always been trial and error. The process that you list definitley makes sence to me in regards to finding the correct nute level. I have always just pushed the levels until I notice issues. This is obviously not best practice. I will use this process until I get it right thanks GG. My goal has always been to have the perfect grow "no deficiencies"
  15. ahh I see, I can see that way working, only problem being is that you only know when you go over when the plant shows damage, by then I guess some damage is done. I'm glad I can help

    when I first figured out this method I assumed that it must be the standard way to do things. but I have looked on forums and gone through half my books (i have a lot of books) and just see people guessing all the time. surely I'm not the first person to figure this out?

    I have used this method with a lowryder#2 in DWC, and I had the cotyledon leaves still perfectly green up until the plant was about 5 weeks old and the stem got so thick it tore them apart. growing in soil is almost impossible to get that level of accuracy. I love hydro, so much easier in my opinion
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  16. I started with soil as well and back then they didnt have meters that would read soil PH and nute levels accurately thats why started in hydro. I've got really good at guessing, but I've always grown the same strain. An original Northern Lights from the early to mid 80's. Oh I forgot to mention I have a 75 gallon rez and I run 6 plants at 4' thats why they drink so much. I use flood and drain, here is a pic of the system I built. On my next round Im going to post a from begining to end grow starting from cutting. Thanks for the help I sould be able to dial it in now

    Attached Files:

  17. Hey Brother,can you give me a little insight,I did my newt change yesterday and after I mixed everything up I checked my PPM"s it was 1329 witch I thought was kind of high, but the water was a little cold 66f so I put the heater in the tank, today I went to check my PP"s againg and it had dropped to 1187 and the plants drank 1 gllon of water, but I forgot the heater was in the tank and the temp went up 11 degrees to 77F can the higher temp have given me an incorrect reading,I took the heater out of the tank (of course) if I wait till the temp goes down will I get a better reading or should I start over,another words should I wait for the temp to go down check PPM"s then wait another 24 hours and test PPM"s again???
  18. Not sure water temps have much effect in ppms.
  19. Thanks sado44,I know water can effect PH levels,and I am ALMOST sure I read some place ( but now I cant find it) that water temps also effect PPM's as well,thats why I am asking,because even though I kind of feel 1329 PPM's is kinda high but from what the readings are telling me is they are not high enough..
  20. Usually the warmer the water the higher the reading and the colder the lower. It also shows it on the hanna calibration solutions. Hope this helps
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