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Targeting nutrient (ppm) levels in Aero/Hydro system

Discussion in 'Hydroponics / Aeroponics' started by jointchief, Dec 17, 2008.


    jointchief Well-Known Member

    I've heard a rumor that PPM levels in an aero setup should stay approximately the same over time. If the ppm levels rise or fall, this mean the target value is off. If your ppm levels are rising, this means that the plants are sucking up more water than nutrients, and the target ppm level should be decreased. If the ppm levels are falling, this means the plants are sucking up more nutrients than water, and your target ppm level should be increased. I thought about this a great deal, but still cannot determine if this a good rule to follow. If it is, does it apply to all stages of growth (except the beginning when you start out with 0 ppm usually)?

    I ask this because my plants right now are in heavy flowering, and they are sucking up way more water, (ppm levels are rising constantly) so maybe I should start backing down on the nutes (lower the ppm)?

    buggs bunny

    buggs bunny Well-Known Member

    i thought if the # goes down then you add more to get back to that #

    700 is all the plant can handle ,ant more is wasting the ferts

    jointchief Well-Known Member

    Maybe I was kind of vague in my initial explanation.

    Of course if the ppm # goes down, you give it more. That is exactly what I'm trying to say. If the ppm level goes down, this means the plant is soaking up the nutrients faster than the water, and requires more nutrients to be added to the reservoir. So you can add more nutrients and target a higher ppm concentration so that the plant will soak up more nutrients with more water so that the ppm level will stay the same over time instead of decreasing. Maybe this is too hard of a concept for most growers...I think this is a correct method, and is a good way to tell what your ppm level should be at a given growth stage.

    Just saying "700 ppm" is all the plant can handle is kind of a very bold statement. First of all you didn't even mention what conversion factor you had in mind (.5, .75, etc.) and second of all, I've seen plants over 10 feet in height that require around 2000ppms (.75 conversion factor) at certain stages.

    My whole reason for this thread, is to try to gather some knowledge about how to determine how much nutes to give a plant at a given stage (veg, transition, flowering, heavy flowering, harvesting, etc.). In my experience, the amount of nutrients the plants need grow bigger and bigger in the veg stage, then get even larger when in flowering, then after most of the bud has developed the nutrient uptake slowly tapers off until no nutrients are taken in by the plants at all and the plants begin to suck in a lot of water instead. My theory is this:

    At a particular growth stage, a plant will consume a fixed amount of water, and a fixed amount of nutrients daily. Because of this, you will see your PPM's (or EC) fluctuate. If the plant takes in a lot of nutrients, and not much water, you will see your PPMs decrease, and you will have to add more nutrients to feed the nutrient hungry plant. When adding more nutrients back to the reservoir, you should add enough nutrients so that the overall PPM is higher than before. This way there is a higher nutrient to water ratio in the reservoir, which linearly matches the plant's current nutrient and water intake RATE. So over time you will notice the water level in the reservoir go down, however the PPM level will stay the SAME instead of decreasing. This is all about rates of change, so if you haven't taken any physics or calculus, you may be at a loss.
    buggs bunny

    buggs bunny Well-Known Member

    i know meters register different but this gut heath on rui somewhere grows the biggest budds i have ever seen in a hydo set up and root balls that you would say no way.and all he recomends is 700ppm and said the plant dosent use the nutreints past 700.

    i dont know about the rest of your question though?

    AeroKing Well-Known Member

    The proper amount of nutrient is incredibly strain dependent. I have some b-52s that show deficiencies at anything under 1200ppm... Really thrive at around 1500ppm...

    jointchief Well-Known Member

    You cannot just say, "oh yes give the plants X amount of ppm". Because if you give a small plant 700 ppm, it will DIE very very quickly. (Especially on a .5 conversion scale).

    Let me try to explain this by example.

    Example 1:

    We have a Aeroponics setup with a 20 gallon reservoir with 14 female plants that are currently 4 weeks into the vegetative growth stage. How much nutrients should be in the reservoir? Obviously, you don't want to add too much or they will burn to death, and you don't want to add too little or they will be deficient. So we go ahead and start small, and add 200 ppm. After a day you notice that the ppm meter reads 150 ppm in the reservoir. So you add more nutrients (in the recommended proportial ratios as listed on the bottle) and bring it up to 300 ppm. The next day you notice the ppm meter reads 290 ppm, so you add more nutrients and bring the reservoir up to 350 ppm. A few days pass by and you notice NO change on the ppm meter, but the reservoir water level has gone done considerably (soaked up by the plants). Why did the PPMs stay the same once the reservoir was increased to 350 ppm? Good question.

    This means that the plants required a target nutrient concentration of 350 ppm so that the nutrient uptake RATE and water uptake RATE of the plants at this particular stage of growth are perfectly balanced. In other words, the plants would consume just enough nutrients, and just enough water keep the current ratio of nutrients to water in the reservoir at 350ppm. This is how you know you are at the right level of nutrients in your reservoir.

    Example 2:

    We have a Aeroponics setup with a 20 gallon reservoir with 14 female plants that are currently 6 weeks into the flowering growth stage. What should the nutrients be at? The ppms are currently set at 800 PPMs. A day passes by, and you notice that the PPMs have increased to 950 PPMs. You add some distilled water to the reservoir, and bring the PPMs down to 700 PPMs. Another day passes by, and you notice the PPM meter now reads 750 ppms. So you add more distilled water to bring the total reservoir nutrient concentration to 600 PPMs. A few days pass by and you notice the PPM meter still reads 600 PPMs. What does this mean?

    Because the PPM level was constantly increasing when the PPMs were at 800, or 700, this implies that the plants were uptaking more water than nutrients. So more water was added to decrease the concentration of nutrients in the reservoir. Once the concentration (when I say concentration, this means the proportion of water to nutrients in the reservoir) was decreased to a target level of 600 PPM, the rate at which the plants were consuming water and the rate at which the plants were consuming nutrients allowed for the 600 PPM concentration to remain constant. This is the correct reservoir concentration for the plants at this growth stage.

    As you can see, using this method is very easy, and it is very easy to apply to any strain, any type of EC meter, or hydro setup. It bases everything on the RATE at which the plants are consuming the nutrients, and water.

    Any comments?
    Tman20 and Someguy15 like this.

    tonylarock Member

    great info thank you

    RemeberMe Active Member

    This is so true it should be a sticky!
    oh really???

    oh really??? Well-Known Member

    Word. This is a very important concept.
    oh really???

    oh really??? Well-Known Member

    Word. This is a very important concept.

    kingme Active Member

    my ppm levels are usually around 2000-2500. Any they are dense and happy as shit. I could not see loweing the ppm to below 1500. I dont know how anyone would get a decent product at 700. Maybe for clones 700. But i personally run my clones at 1000 and they thrive.

    jhonblaze Member

    I'm currently growing sour diesel DWC 6 plants at 1500 + ppm during week 4 of flower and they are thriving. They suck up more water then nutrients, does this mean i should lower the ppm?? im confused. They are thriving and i was under the impression that the water to nutrient ratio should NOT be equal. The plants take up much more water then nutrients. So keeping your nutrients at high levels without signs of stress is what you should aim for. Also changing your reservoir every week is a necessity to guarantee the plants get all the nutrients they need. By changing the reservoir you replace specific nutrients the plant may have used more then the others. someone please confirm this Idea as this thread has confunded me. )))

    Happy Turkey Day mmmmmm weed and turkeyyy

    PocketsOnSwole Active Member

    thanks for sharing this info with us, it really helps a new hydro grower like me! :leaf:

    jjfoo Active Member

    I can. I read a study on flowers that concluded that the sweet spot for EC is large. Like if you are within 1.5 - 3 (I don't recall the exact numbers) that you would get similar growth. To low you get deficiencies, to high you burn your plants. I think this science gives us the best clue as to why people say they get results low and high. It is predicted to be this way...

    jjfoo Active Member

    Lowering the EC could make it easier for you plant to uptake water via osmosis. If they are not consuming these nutes then I doubt it will harm them to lower it. Consider it like steering a big ship. You want to give it what it needs to stay on course. Small corrections.

    I have some plants that have no runoff at all. If I don't monitor the EC they will either accumlate salt or become deficient. I never drain my runoff. With coco and DWC. I use really pure nutrient salts and RO water. No organic substances go in my res apart from bits of coco that collect, but coco decomposes really slow.

    jjfoo Active Member

    Yes, I have a comment. I do this exact thing. The plant calls for nutes. It can be measured and is %100 objective. How much simpler could it be, yet there seems to be much confusion... I think you summed it up.

    mindphuk Well-Known Member

    I'm thinking I prefer to have the TDS drop so that when I top off, I add fresh nutes. The reason is that TDS is a measure of all of the ions in solution, but the plants may be requiring some more than others. IOW, you can still have your PPM on target but still show a deficiency because maybe potassium and calcium are being taken up more quickly than others so unless you are adding fresh supply of balanced nutes on a regular basis, they can be very unbalanced by the time you do a rez change. As long as I'm supplying sufficient quantities, nutrients shouldn't be a limiting factor in growth, hence the large sweet spot for EC value.

    Thebogie Member

    I like the ship analogy. I am a pilot so small changes AND stay ahead of the damn winged thing so you don't bend it! LOL

    jjfoo Active Member

    I water my plants with no run off at all. I don't see what your idea would be predicting. I am seeing growth equal to my drain to waste systems. I have a bucket in a bucket with a wick. The wick not only allows the run off to soak up but more importantly removes the perched water table that would normal exists in any pot due to capillary action. With out a wick to drain there will always be a saturated layer at the bottom. Like a giant bead of water... You can drain it watch it drain with my inserting a toothpick after you have stopped getting run off. It is not good to have to roots flooded at all and container plants get this way unless you have a way for the water table to drain.

    but back to the point... I used to think that I needed to flush out the old nutes because they where unbalanced. I am using a Jack's pro hydor and calcium nitrate from roots to flowers. And of course I'm using RO. I wouldn't recommend this with tap water. Some of the minerals in tap water may accumulate and then you could have issues like you predict.

    I would like to take my runoff to get sent for an analysis and compare it to my watering res to see if how far it deviates. It might be more of an issue on long term container plants that stay in containers for years not 8-9 weeks on avg.

    mindphuk Well-Known Member

    I think that's key. If you can run as well as drain to waste. I think that would be the gold standard to shoot for.

    [I'm running recirculating aero/nft btw]

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