COCO COIR Large dry spots on leaves. No pests detected. Please help

[ShimmyBob]

So could really use a few opinions.
It's an LED setup in Coco, 2x 220W full spectrum LED panels (though heavy on the red and blue)

Temps range from 23 to 28°C or 73.4 to 82.4 °F
Humidity between 35 and 50%, even though it's way higher outside due to the constant rain. Had to get a dehumidifier which you can see in the background.

They get watered every 3 to 4 days, depending on how dry the medium feels, and nutrients with every other watering.

I'm sticking to the recommended doses on the GHE trio plus Calcium and Magnesium supplements, since I don't feel comfortable venturing too far from the tried and true yet. Additionally, I'm adding some Diamond Nectar, Bio Root and occasionally some Alg-A-Mic. I do have some Trace Mix from Canna in case it's something obscure like Molybdenum deficiency as well, but until I get some second opinions on what this is I'm not using it. Didn't need any on the last Coco run (which was also my first in Coco and second run overall). Those plants also displayed signs of this problem shortly before harvest, but nowhere near as bad as here, and not as early in growth.

Could this just be light burn? Panels are about 22 inches from the top leaves. Or am I underwatering the ladies somehow, maybe if their roots aren't reaching low enough yet?



EDIT:

Hey Bob ,you been checking PH ??

Oh sorry, I forgot to mention that. I'm using a digital bluelab PH meter and doing a calibration every 2-3 weeks. PH of my nutrient solution and plain water is always in the 6.0-6.1 range.

[D.A.A.S.69]

Hey Bob ,you been checking PH ??

[Aloner]

Leaves don't look like they're drooping at all, which is always the first symptom of underwatering my plants have shown.

[ShimmyBob]

Hey Bob ,you been checking PH ??

Oh sorry, I forgot to mention that. I'm using a digital bluelab PH meter and doing a calibration every 2-3 weeks. PH of my nutrient solution and plain water is always in the 6.0-6.1 range.

[Mr.furley]

Hey bob,
how about a picture of the whole plant(s) in natural light? Is it just 1 plant, 1 leaf? Could you have spilt water on your leaf.
is that your coming out Ph or just your going in Ph?

does look a like burnt and crispy on the leaf, could be the lights to close but I'm not a Led light guy. IV heard 18"-30" for those guys.
My other thought if your coming out Ph is @ 6.o-6.1 is to adjust your PH up to 6.3-6.5 nutrients absorbed at different ph. Maybe your missing your cal-mag or others by staying at 6.ph.

[ShimmyBob]

Hey bob,
how about a picture of the whole plant(s) in natural light? Is it just 1 plant, 1 leaf? Could you have spilt water on your leaf.
is that your coming out Ph or just your going in Ph?.

Added an image of the plant that has it worse plus a close-up of one of the really bad spots. Natural Light is tricky since I have very weak lighting outside the tent. Camera flash is the best I can do.
It's 2 plants in all and it seems to affect the larger, older fan leaves the most, but the spots do show up all over the plant.
Some water gets on the leaves occasionally, but I always gently shake it off and with the relatively low humidity any remaining drops evaporate away within an hour.

PH is the PH going in, never tested the runoff.

As you can see on the pictures, The girls have been topped 5 or 6 days ago. I'm planning on a long veg phase and I'm waiting for them to grow large enough for me to LST them into a manifold and then top some more.

[Mr.furley]

Bob, I would Check your out PH next water, that's the one you go by! If it's off your roots are at the wrong PH, check that before adding/removing nutes and such.
Is the spots in the center of the tent?

[ShimmyBob]

Bob, I would Check your out PH next water, that's the one you go by! If it's off your roots are at the wrong PH, check that before adding/removing nutes and such.
Is the spots in the center of the tent?

Sure I'll try testing the runoff next watering.

The spots aren't localized, they're all over the plant (and both have them, only one more than the other, and it's seemingly more severe on the lower leaves.

[ellz]

To me, it kinda looks like boron deficiency: http://www.growweedeasy.com/boron-deficiency-cannabis

[Aussiebloke]

Ive been doing some research and ventured down to a few local hydro shops, they seem to think it's from overwatering??? I tend to agree as i have no mites or bugs flying around... no visible sign of nute burn and it has signs on all 4 of my plants in various degrees... might be of some help as i think i may have went overboard with the watering as i never had this drama in smaller pots till now in the bigger ones. Let me know what you think?

[D.A.A.S.69]

You pick up your pot to tell if it needs water.

[Sheesh]

Looks like you have the basics covered. What about the coco? Is it a proven brand and were the salts rinsed out well?

[ShimmyBob]

Looks like you have the basics covered. What about the coco? Is it a proven brand and were the salts rinsed out well?

Coco is all UGro bricks plus perlite. I don't think it's any kind of residue, since I've watered a couple times since planting and these spots have only started to show up about 10 days ago.

Can't imagine it being overwatering either, since I always feel if the substrate is still wet before watering.

I can't help but think it's some kind of nute burn. No clue what it could be though. It also looks a bit like super heavy wind burn, but I toned down the fans as soon as the first spots started appearing, and for the past week they haven't been getting any direct breeze at all. The spots aren't just brown, they're downright crispy to the point where immediately crumble when I pinch them.

[ShimmyBob]

Update:

Alright, I just got home from work and there's positive news. Looks like it was either some really weird nutrient lockout or the PH wasn't right. I've been giving them plain water PH'd to around 6.2 for the last two waterings, last time yesterday, and the problem seems to have resolved itself. Just since the watering yesterday they've grown amazingly fast.

It's not even been 24 hrs since I last checked on them, and they seem to have almost doubled in size. The necrosis obviously won't recover, but there's a ton of new growth to make up for it. I'd say some very careful LST next, maybe another watering with just plain water and they should be good. I really hope this was it...

[Mr.furley]

So bob, what was the runoff PH at?

[Sammy]

Not over-watering if you're using cocoa I water my plants daily sometimes twice a day the king of over-watering doesn't seem to affect my plants and Coco they love it. Definitely looks like the pH was off at the roots, get used to checking your runoff especially after having problems my experience has been while vegging pH seems to rise flowering my pH seems to drop. Good luck ☮️

[stevenics]

make sure your ph meter is calibrated, i calibrate mine before EVERY SINGLE use, and i test it against the regular liquid chemical reaction PH tester, so i know it is correct and therefore can get a more exact PH in my reservoir. . Definitely check the PH of the runoff like mcfurley said, it will tell you if you are having ph problems in your soilless mix. btw, i also use a bluelab ph tester, a pretty expensive one, they say to calibrate it weekly depending on amount of use, but from past experience i know to calibrate it every time before using it.