Nutrient PPM Dosage Theory

Hemp/CBD bagseed
5 gal DWC
Age: 58 days, week 2 flower
Light schedule: 18/6 (apparently she's an auto)
DLI: 25
VPD: 1.3

I first tested this 2 days ago based on my most recent ppm measurement (day prior) and was expecting a ppm reading of 1250, it read 1150. That's only an 8% difference so I figured fuck it that's close enough to look further into it.

3 gal = 588 ppm (fresh res)
2 days later
1.5 gal = 769 ppm
"Ate" = 386 ppm
Desired PPM = 535

To get the 1.5 gal in the res from 769 to 535 the 1.5 gal top off solution should be 301. To dose the 1.5 gal with 301 of nutes I cut the dosage down to 25% strength of what I mixed to get my starting res of 588.

After Mixing the top off solution the ppm was 332. Mixing 1.5 gal of 332 to 1.5 gal of 769 should be 550. It measured 566, close enough.

So in theory she will drink the same 386 plus, I'm guessing, a little extra as she gets older. If this holds true we can calculate, within a reasonable degree of accuracy, how much water vs nutrients each individual plant is taking up and adjust accordingly.

Even though I calculated that she ate 386 ppm, I didn't want to drop the ppm that low because she doesn't seem to mind it where she is.

Once I get a baseline of how much she's eating I plan to start adjusting variables to see what happens. My first move is to increase the DLI to see how it effects nutrient uptake. From what I've read, higher DLI should mean more nutrient uptake but I'd like to actually put a number to it. I'm going to increase DLI by 5 on a weekly basis on the same day as the res change. Once she starts to show signs of stress I will back off a little and leave the DLI alone.

Next I plan to adjust VPD to see how it effects the nutrient uptake, then I'll consider adding CO2. This obviously won't all be done with this same plant. The initial testing will be done one her but they next seed I plant is going to be a feminized CBD photo. Ideally I will keep her in veg long enough to test everything mentioned above. The goal is to put together a calculator where you can input your environment parameters and get an accurate reading of your plant's needs. No more guessing!

Any input is greatly appreciated. Is there something I'm not considering? Has anyone tried something like this before? I spent multiple evenings trying to get some information on this but I got nothing.


TLDR: The goal is to put together a calculator where you can input your environment parameters and get an accurate reading of your plant's nutrient needs. No more guessing!

I feel like there are so many variables even within the same strain, let alone multiple, that this would be a daunting task. If you can do it, you are way smarter than I am.

So far it's been working out very well. I made a spreadsheet to calculate everything so I only need to tell it res Volume, top off amount, current ppm and desired ppm. It calculates your desired ppm based on starting ppm and volume vs current ppm and volume, it tells you exactly how many ppm she ate per falling. For example last week she drank more water than nutes and ppm jumped past 2000 so my top off was only 240ppm and I got my goal of 800.

The closest I've ever gotten to that in DWC was to top off with RO to calculate the ppm drop. I then had a factor number to add just enough nutrients only to bring ppm back up to my target, no supplements included.

Now in RDWC, I make enough extra solution to top off during the week and then do a total replacement every week.

Addie42069 said:

TLDR: The goal is to put together a calculator where you can input your environment parameters and get an accurate reading of your plant's nutrient needs. No more guessing!

Click to expand...

Sounds like a great plan. Now lets talk about data sets and statistics.

Your idea is a good one but based on your goal to integrate most aspects of growing into the "app " as we shall call it gives us a truly breathtaking amount of data that needs to be gathered. Add into it topics like phenotypes which are freakin huge and well this is just going to get unwieldy.
An estimate of date points needed for the following:
Nutes ppm
water amount
time ( most people forget this one )
lights
vdp ( we can encorporate RH and temp here to save time.)
sensor drift
sensor calibration
co2 ( you mentioned this)
At this point we can just follow the math. we have a basic level of date points that will develop data streams. We have 8 points creating the stream
Data points are math. Math can be proven when working with statistics. For these 8 streams you will have to generate over 80,000 entries into your formula to get workable data. Some of these will go quickly like ph control and nutes. The real rub will be the VPD and co2. currently no grow kit manufacturer puts out sensors for temp and RH that will give useable data sets. Right on the box they state +-3% So is my RH 67 or 64? is my temp 77 or 73? Now look at you vdp chart and see what that mess looks like.

I am not trying to piss on your idea but you seem ernest in you idea and I do think it would be useful. Right after the error and drift for sensors is fixed. Might wanna start a go fund me page for the data stream generation. You will need help.