What’s the issue and how can I fix it?

Hey, I’m running into a problem with my current grow, and I can’t quite figure out what’s going on. So, I’ve got the plants in 5-gallon pots, using Jack’s 321 nutrients and Power C silica. They’re on a 12/12 light cycle, just switched to flowering about 48 hours ago.

The issue? I’m seeing yellowing leaves, some wilting, and a few rust-colored spots on the fan leaves. I’m watering through drip irrigation twice a day until runoff, but thinking about bumping it up to three times.

I think it might be a CalMag deficiency. I say that because I don’t think I properly buffered the coco. I did soak it in CalMag, but I didn’t pH the water above 6.2 like I should’ve. Anyway, just wanted to see if anyone here has any ideas or thoughts. Could really use some input!

First check under the white, mottled leaves for mites, use a loupe.

curious2garden said:

First check under the white, mottled leaves for mites, use a loupe.

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So, I didn’t notice any mites, but I used the opportunity to take some close ups of the spots.

Looks like a cal-mag issue.
I use coco/perlite and usually pre buffer by soaking in a cal-mag solution of 3ml/gal water. Then rinse with 6.0-6.2 water. I also use Jacks 321 and will use cal/mag if I see a problem at 3ml/gal due to my well water having very little magnesium in it.
I attached a nutrient availability chart so you can see how ph affects absorption. I think adding cal/mag to your jacks and making sure your final ph is 6.0-6.2 would help. You might even want to go 6.5 for a few feedings.


What ec are you running for you Jacks?

I wanted to add a easy way to buffer the coco.
I use two 5 gallon buckets.
1 of them has a bunch of 1/4" holes drilled in the bottom. Then I have 1/8" mesh wire (I think they call it hardware cloth) in the bottom. I then insert this bucket in another 5 gallon bucket that is unaltered. Add the coco coir and pour the cal-mag water in there for the soak then the next day I just lift the inner bucket with the holes/mesh out and let it drain. Then without the unaltered bucket just rinse the cal-mag soaked coco with the water that has been ph adjusted. Let it drain good and it's ready to go.

RottyRzr said:

Looks like a cal-mag issue.
I use coco/perlite and usually pre buffer by soaking in a cal-mag solution of 3ml/gal water. Then rinse with 6.0-6.2 water. I also use Jacks 321 and will use cal/mag at 3ml/gal due to my well water having very little magnesium in it.
I attached a nutrient availability chart so you can see how ph affects absorption. I think adding cal/mag to your jacks and making sure your final ph is 6.0-6.2 would help. You might even want to go 6.5 for a few feedings.
View attachment 5433752

What ec are you running for you Jacks?

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I haven’t been adding any calmag at all to Jack’s because I assumed there was enough already in it. I use RO water so there’s absolutely none in it.

As far as EC, I started around .85 during early veg and worked my way towards 2.2 towards the end. Right now I’m currently feeding with the “Bloom” with Epsom only that came in their kit to induce flower formation, aside from Power Si.

The plant in question is Afghan Kush, I have a Honey Cream right next to it getting the same exact nutrients at the same strength, time and duration that isn’t showing these symptoms.

I would increase feeding frequency. Most common fix for a Ca/Mg problem with plenty of both in the medium is to raise pH of the input.

I would raise topH 7.0 until you see improvement and then dial back to pH 6.5.

Wastei said:

I would increase feed frequency. Most common fix for a Ca/Mg problem with plenty of both in the medium the problem is low Vio availability and accessibility. The first thing to do is to raise pH on the input.


I would raise topH 7.0 until you see improvement and then dial back to pH 6.5.

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I will be increasing the feed frequency. The medium is coco/perlite and I’ve read to treat it like hydro and keep ph between 5.8 and 6.2

GrindMind said:

I haven’t been adding any calmag at all to Jack’s because I assumed there was enough already in it. I use RO water so there’s absolutely none in it.

As far as EC, I started around .85 during early veg and worked my way towards 2.2 towards the end. Right now I’m currently feeding with the “Bloom” with Epsom only that came in their kit to induce flower formation, aside from Power Si.

The plant in question is Afghan Kush, I have a Honey Cream right next to it getting the same exact nutrients at the same strength, time and duration that isn’t showing these symptoms.

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2.2 EC is rather high with 321.
What is the "bloom" and the kit you refer to? There is no bloom in jacks 321, it's part A, calcium nitrate and magnesium sulfate, aka epsom salt.

My good friend, the kit I speak of is posted on their site and additionally on the Jack’s 321 feed chart. There is indeed a bloom bag of nutrients included in the Jack’s 321 kit.


It is to be used for the first week after switching the light cycle to 12hrs for photoperiod plants to help induce bud period and formation.

As far as EC, what level would you suggest and advise for Jack’s 321?

Just run the main 3 part and use the rest to fertilize the lawn. I just harvested using Jacks and rainwater and the plant had green leaves right to the end.

7CardBud said:

Just run the main 3 part and use the rest to fertilize the lawn. I just harvested using Jacks and rainwater and the plant had green leaves right to the end.

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if you don’t mind, I have a couple questions.. what size pots were you using, which medium and how frequent did you water/feed. Also what was the usually EC that you fed at?

GrindMind said:

My good friend, the kit I speak of is posted on their site and additionally on the Jack’s 321 feed chart. There is indeed a bloom bag of nutrients included in the Jack’s 321 kit.

View attachment 5433849View attachment 5433850View attachment 5433851View attachment 5433852
It is to be used for the first week after switching the light cycle to 12hrs for photoperiod plants to help induce bud period and formation.

As far as EC, what level would you suggest and advise for Jack’s 321?

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I hadn't seen that kit before. I just use the 5-12-26 part A, 15-0-0 part B and epsom. I use around 1-1.6 EC with coco in 2 gallon pots, but there are variables like pot size and fertigation frequency etc. I've started to use MaxiBloom in flower but still run 321 for veg.

I was in peat mix, either Sunshine #4 or Berger BM6...I can't remember now. I usually watered once a day at around 1.4EC, during heatwaves I would water twice a day at 0.8 EC. Final pot size was 7 gallons.

I’m still kinda new to this, I had a few harvests a few years back but they were all in hydroponics, this is my first experience in coco.

I did notice that I had some red stems and I also remember reading somewhere that it isn’t a good thing. Hopefully this could be another symptom that could bring some insight of what the issue could be.

Looks like pH issues. Why 6.2 for coco? That’s soil.

5.5-6 is coco. Fix pH first wait a week or so (check new growth) that’s what I would do

Nutty sKunK said:

Looks like pH issues. Why 6.2 for coco? That’s soil.

5.5-6 is coco. Fix pH first wait a week or so (check new growth) that’s what I would do

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I usually always adjust my PH to 5.8 but all the research I’ve done says that calcium is best absorbed at 6 or a few points over.

7CardBud said:

Just run the main 3 part and use the rest to fertilize the lawn. I just harvested using Jacks and rainwater and the plant had green leaves right to the end.

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Same experience here. I run the three part and it's just fine.

curious2garden said:

Same experience here. I run the three part and it's just fine.

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Can I ask which medium you use and which size pots, the EC in which you feed at and what your final PH you adjust to?

GrindMind said:

Can I ask which medium you use and which size pots, the EC in which you feed at and what your final PH you adjust to?

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Coco/perlite, drain to waste in 2 gallon Floraflex pots for flower. My EC today is 1.25 but my plants are little hungry so right now I'm fertigating 3x/day until I add more nutrients to my reservoir as my plants would prefer 1.5ish. I pH to 5.8ish after the bounce and it usually swings up to 6.3 by the time I'm finishing up the reservoir, about a week.