Help me decipher PPM readings, please.

CannaDana · Mar 28, 2022

Hi! I need your help.

Today for the first time I checked the PPM coming out of my plants. I have two strains, both in Fox Farms soil. They are in mid-flower. One strain's leaves are dying off, and I thought it was a little soon, so worried I might have a lockout. So I checked one plant from each variety. Here's what I found:

WATER GOING INTO PLANTS: 220 ppm
WATER COMING OUT OF KUSH MINTS (the "good" plants): 980 ppm
WATER COMING OUT OF GG4 (the "dying" plants): 630 ppm

What does this mean??? The plants I thought were fine are reading 2070. The plants I feared were locked out are reading 630 ppm. Both varieties get fed the same amount at the same times. So, questions:

1. What does this mean in terms of salt build-up in the soil?
2. How can the two strains be so completely different in runoff?
3. What do I need to do, if anything?

Here are photos.

GG4, the “dying” 630 ppm plants (the saggy leaves are more due to me letting them dry out to get the truest reading I could):

Kush Mints, the “good” 980 ppm plants:

What's the answer? Often, I think the best answer is "do nothing." I'm very confused by these results, though.

Thanks for your insights, you guys really help!

CannaDana · Mar 28, 2022

My instincts tell me I should feed the GG4 more than I have been, and not feed the Kush Mints anything but plain water. Is this the right answer?

Does the fact that PPM is more coming out than going in mean anything important?

Maxwax · Mar 28, 2022

Im new but I agree. That PPM is twice what it should be on the Kush and lower than it should be on the GG4. You can even see the nitrogen and probably potassium deficiency clearly. Since the GG is looking ok that hot I wouldnt flush....yet so yeah straight waterings. Are you positive those numbers are correct?

CannaDana · Mar 28, 2022

Maxwax said:
Im new but I agree. That PPM is twice what it should be on the Kush and lower than it should be on the GG4. You can even see the nitrogen and probably potassium deficiency clearly. Since the GG is looking ok that hot I wouldnt flush....yet so yeah straight waterings. Are you positive those numbers are correct?

No, they were not correct. I was wrong about the Kush Mints. I retested and Kush Mints (bottom) were at 980 while GG4 (top) was still at 630. I have edited the original post to reflect the correct numbers.

I want to emphasize that these are numbers I'm getting when I put in plain water, which has 220 ppm. So, the Kush Mints runoff is more than 4 times the ppm of the water that went in, while the GG4 was around 3 times the ppm going in. I have no idea what significance that has, if any. I'm brand new to this.

Maxwax · Mar 28, 2022

CannaDana said:
No, they were not correct. I was wrong about the Kush Mints. I retested and Kush Mints (bottom) were at 980 while GG4 (top) was still at 630. I have edited the original post to reflect the correct numbers.

I want to emphasize that these are numbers I'm getting when I put in plain water, which has 220 ppm. So, the Kush Mints runoff is more than 4 times the ppm of the water that went in, while the GG4 was around 3 times the ppm going in. I have no idea what significance that has, if any. I'm brand new to this.

I dont either, thats interesting. Tighter packed soil? IDK.

phxazcraig · Mar 28, 2022

I wish I knew. I'm seeing weird PPM/EC runoff in my plants ever since they went into flower. Before then my runoff EC/PPM was lower than the input, indicating plants hungrily devouring all the nutes.
In flower my runoff PPM is much higher than input. Because I'm growing in coco, watering is different, but maybe it's like soil but faster. In that case I might give some useful data points. I tried flushing, mostly by just running 4x the usual watering at one event. I'm already watering/fertilizing 5x daily with more than 20% runoff, yet my PPM was still building up.

The 'flush' helped lower the runoff quite a bit, but it just kept rising 50ppm per watering. I next tried increasing the amount of water each event, from a 25-second watering to a 45-second one. My water/nutes use went through the roof, and I had about 75% runoff. Yet the PPM still rose.

Next I tried lowering the input PPM, a lot. That worked, so I'm continuing along that line. My guess is I have a lot of evaporation going on since I added a powered input fan blowing more-or-less on the pots. My thinking is that I may be putting in an input of X PPM and getting a runoff of 1.5x, so the roots must be seeing even higher than 1.5x. I'm seeing tip burn indicating that plants are seeing too much PPM even with a fairly tame input dose.

Being coco, I have tools you don't in soil, and one is increasing frequency of waterings. I'm now trying 7x daily waterings, with times cut to add to the old total of 5x. I want to see if I can balance out evaporation this way, if that's what is going on. In soil, I think the only good approach may be a long stretch of lower-dose waterings, possibly preceded by a bit of a flush if things were toxic. But your plants don't look too bad, so I'm thinking no flush. Why plants side-by-side react so different? No idea.

steamroller · Mar 28, 2022

I would feed the gg. I agree with Max on k being needed . I have plants doing the same now .
To really know what is excess run off you need to know what the water does through fresh soil.
Then you could have a base . Then you could know if either was high or low .

growsince79 · Mar 28, 2022

CannaDana said:
No, they were not correct. I was wrong about the Kush Mints. I retested and Kush Mints (bottom) were at 980 while GG4 (top) was still at 630. I have edited the original post to reflect the correct numbers.

I want to emphasize that these are numbers I'm getting when I put in plain water, which has 220 ppm. So, the Kush Mints runoff is more than 4 times the ppm of the water that went in, while the GG4 was around 3 times the ppm going in. I have no idea what significance that has, if any. I'm brand new to this.

Check out the runoff of new ff soil. Mine varies from 2000-3000ppm.

Madbud · Mar 28, 2022

I don’t like measuring runoff in soil, do a slurry test. Sounds like salts building up for a good flush.

Grapefruitroop · Mar 29, 2022

Yeah , measuring PPM in soil is a waste of time.....
PPM readers, measure the level of dissolved solids ina liquid....is used in soilless medium to calculate the total amount of nutrient that you aim for....
In soil you have too many dissolved solid that arent nutrients so you arent calculating the amount of nutrients but them togheter with other unknown particles....like....mud.. etc...

Long story short....measuring runoff will be very decieving and confusing.....leave it for the hydro peeps

Another point to consider is that you are using a mix that have peat in it, that means you have a pretty good CEC level that will keep some nutrient bond to the soil and the water will be unable to flush em away.....another reason why analizyn the runoff of a soil grow is not helpful....

Grapefruitroop · Mar 29, 2022

BTW the plants looks good, normal fading to me.....maybe start to decrease nutrients in the ones that looks more dark greeen

Edinburgh · Mar 29, 2022

You check your pH by the runoff, an electric pH meter will tell you your pH, mine is 6.2 but a cannabis plant can handle a pH of 5.8 to 7.00 but that is not optimal, in other words your meter is converting nute part per mill and converting it to a pH reading.

CannaDana · Mar 29, 2022

Grapefruitroop said:
Yeah , measuring PPM in soil is a waste of time.....
PPM readers, measure the level of dissolved solids ina liquid....is used in soilless medium to calculate the total amount of nutrient that you aim for....
In soil you have too many dissolved solid that arent nutrients so you arent calculating the amount of nutrients but them togheter with other unknown particles....like....mud.. etc...

Long story short....measuring runoff will be very decieving and confusing.....leave it for the hydro peeps

Another point to consider is that you are using a mix that have peat in it, that means you have a pretty good CEC level that will keep some nutrient bond to the soil and the water will be unable to flush em away.....another reason why analizyn the runoff of a soil grow is not helpful....

Thank you. This makes total sense to me. Not sure why someone here told me I needed to do this. I thought it might be a waste of time in soil, as what you said seems obvious.

SmokinJo421 · Jun 21, 2022

CannaDana said:
My instincts tell me I should feed the GG4 more than I have been, and not feed the Kush Mints anything but plain water. Is this the right answer?

Does the fact that PPM is more coming out than going in mean anything important?

Check out this video on YouTube
The channel is "grow your greens"
And I found it by searching that channel by 9/11 rule. They break it down in an understandable way.

Help me decipher PPM readings, please.

Help me decipher PPM readings, please.

CannaDana

CannaDana

Maxwax

CannaDana

Maxwax

phxazcraig

steamroller

growsince79

Madbud

Grapefruitroop

Grapefruitroop

Edinburgh

CannaDana

SmokinJo421

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