Troubleshooting new COB grow

Sureshot2 · Jun 16, 2017

Hey all, so I built a COB fixture using 8x citi 1212 3500k 90cri's for my 4x2' tent. The lights at the time were being driven at ~50-52 watts each and the fixture has been roughly 10-12" from the canopy for most of the grow. At around week four or so I started noticing some rusty spots on the leaves directly under the lights, along with a small of amount of twisting/deforming. I initially thought this might be a cal or mag issue and increased the amount of calmag in my RO water to around 200ppm per gallon, but this didn't seem to help at all. By week 5 the rusty spots starting turning into leaf tips getting brown and crispy, eventually moving down the whole leaf, as well as many leaves starting to canoe on a different strain in the tent.

I have been told differing thoughts by various people, some saying it was a temperature/rh issue (VPD??), some saying the lights were too close/needed to be dimmed and others saying it was a lockout issue (I don't think this is the case). Before this grow I was using T5's using the exact same regimen/environment with no issues which is as follows:

3 site RWDC
pH ~5.7-6.1
PPM during veg ~550-600, flower ~650-750 (0.5 scale)
Nutes are GH Flora Duo + Calmag (using RO water)
Additives include Floralicious+, Mammoth P, KoolBloom (Liquid from weeks 3-7, dry from 8-9)
Res is non sterile using Heisenberg based tea
Temps on average are around 75-80f, RH is around 45-50%.
Res gets changed every 2 weeks.

After some suggestions from a friend I dimmed the lights from 50-52W per/sqft to around 40 during week 6, but obviously at this point damage was already done. There was also a point between week 2-4 where the temps were hitting 85-90 on some days due to some warm weather and AC being out of service. At this point I'm not worried about this crop since I'm already in week 8, but I'd like to narrow down what the exact problem was during this grow so I can avoid these issues on the next grow. It does seem like the damage hasn't gotten any worse after dimming the lights, but this could just be a coincidence?

Here's some pictures from a week or so ago:

Sorry if there's any information missing, I'm pretty tired right now. I can grab some more pictures if needed tonight.

a mongo frog · Jun 16, 2017

Sureshot2 said:
. At this point I'm not worried about this crop since I'm already in week 8, but I'd like to narrow down what the exact problem was during this grow so I can avoid these issues on the next grow.

Just my suggestion after reading and looking at the pics, drop the liquid cool bloom. Not sure why the Mammoth P, or the Floraliciuous+. If you saw temps in the 90's then its time to address that (running latter in the evening may help).

CobKits · Jun 16, 2017

50W per square foot is a ton of light. maybe RDWC can keep up, maybe not. most people run cobs at 30-40 W/SF

75-80F is on the lower side of temp, maybe they arent transpiring enough and exasperating your cal uptake

Sureshot2 · Jun 16, 2017

a mongo frog said:
Just my suggestion after reading and looking at the pics, drop the liquid cool bloom. Not sure why the Mammoth P, or the Floraliciuous+. If you saw temps in the 90's then its time to address that (running latter in the evening may help).

I started running the Floralicious+ and Mammoth P based on recommendations from several other friends running hydro/rdwc since I'm running bennys and not a sterile res. The temp issues has since been addressed with AC and changing the lights on time to at night. I do think I'm going to drop the liquid koolbloom since I don't see it doing much and it causes the pH to go up.

CobKits said:
50W per square foot is a ton of light. maybe RDWC can keep up, maybe not. most people run cobs at 30-40 W/SF

75-80F is on the lower side of temp, maybe they arent transpiring enough and exasperating your cal uptake

This is what I figured, so hopefully turning the lights down to 40W/SF will be better? I had always been told to keep temps under 80f, should I be letting it climb higher? I'm adding about 2 gallons a day to my res with 3 plants growing.

CobKits · Jun 16, 2017

Sureshot2 said:
This is what I figured, so hopefully turning the lights down to 40W/SF will be better?

if youre having stressed plant problems it might be the best thing you can do. i assure you that you can raise a bumper crop if you start at 30W/SF and bump up slowly from there and watch their response

Sureshot2 said:
I had always been told to keep temps under 80f, should I be letting it climb higher?

thats an HID rule, where the leaf temps would be naturally higher due to the massive amount of IR in the spectrum. with LEDs you have more room at high temps. id shoot for 80-85 at 60% RH and see what that does for you

Sureshot2 · Jun 16, 2017

CobKits said:
if youre having streed plant problems it might be the best thing you can do. i assure you that you can raise a bumper crop if you start at 30W/SF and bump up slowly from there and watch their response

thats an HID rule, where the leaf temps would be naturally higher due to the massive amount of IR in the spectrum. with LEDs you have more room at high temps. id shoot for 80-85 at 60% RH and see what that does for you

Thanks for all the info and quick replies. I'll start out lower as you suggested on my next run and raise it to the sweet spot. I wasn't aware about that for LEDs, I figured there would be some learning to do with the COBs, I'll try to raise the temps up a bit. I have a hard time raising the humidity though since the house air is pretty dry from AC always running, and a regular household humidifier will raise me up a few points at best even on high.

HydoDan · Jun 16, 2017

I am having a very similar experience..I added two cobs to my frame in early may for a total of 8 @ 50 watts in a 2x4..
When I hung the light I put it at 16" and left the reflectors on.. Apparently this was too much.. I'm in week 9 so Its almost done.. One plant is way worse than the others.. But yea lesson learned about led power..

a mongo frog · Jun 16, 2017

Sureshot2 said:
I'll try to raise the temps up a bit.

Up a bit to what? Be careful man. Around 80 or a fuz lower is perfectly fine under any type of lighting.

Sureshot2 · Jun 16, 2017

HydoDan said:
I am having a very similar experience..I added two cobs to my frame in early may for a total of 8 @ 50 watts in a 2x4..
When I hung the light I put it at 16" and left the reflectors on.. Apparently this was too much.. I'm in week 9 so Its almost done.. One plant is way worse than the others.. But yea lesson learned about led power..

Sounds like it's definitely an issue with it just being too much light then. Did you get the same brown/crispy leaves from this? My harlequin plants are definitely taking it a lot worse than my starfighter, which is showing minimal stress compared to the harlequins. Despite all the problems the buds themselves seem to be filling out nicely and are very dense, I'm still hoping for a decent yield.

a mongo frog said:
Up a bit to what? Be careful man. Around 80 or a fuz lower is perfectly fine under any type of lighting.

I'll try to keep it closer to 80ish. Right now I'm averaging 75, peaking towards 78 or so for a few hours and then going down to 68-70 during lights off. Water temps are always stable between 66-67f.

hillbill · Jun 17, 2017

Do the symptoms occur on leaves that are close to the lights but not in direct light themselves?

mefunky · Jun 17, 2017

I get those symptoms on leaves that are about 6 inches directly under a cob. If they are off to the side of the cob they can get about 4 inches away before symptoms show up. I'm running 38 watts a sq/f , upper canopy Temps are about 82°f humidity about 50% give or take 1%. I don't think it hurts yield much , but I don't have anything to base that assumption on. I'm getting rite at 2 zips dry per sq/f so I think I'm doing OK on yield. I think there is a lot to be learned yet on cob lighting. Hopefully my experience helps .

KonopCh · Jun 17, 2017

CobKits said:
if youre having stressed plant problems it might be the best thing you can do. i assure you that you can raise a bumper crop if you start at 30W/SF and bump up slowly from there and watch their response

thats an HID rule, where the leaf temps would be naturally higher due to the massive amount of IR in the spectrum. with LEDs you have more room at high temps. id shoot for 80-85 at 60% RH and see what that does for you

As Cobkits said. I have 29-32°C in tent and my plants looks really good and happy. Just try to get as close to optimal VPD as you can.
And with that temp you can also fed more lightly because plants need more water than nutes.

Sureshot2 · Jun 17, 2017

hillbill said:
Do the symptoms occur on leaves that are close to the lights but not in direct light themselves?

The symptoms are definitely worse in areas directly under the lights, but they are mostly apparent on the enture canopy at the top. However, going down just a few inches below the canopy top where it is partially shaded there are no symptoms.

mefunky said:
I get those symptoms on leaves that are about 6 inches directly under a cob. If they are off to the side of the cob they can get about 4 inches away before symptoms show up. I'm running 38 watts a sq/f , upper canopy Temps are about 82°f humidity about 50% give or take 1%. I don't think it hurts yield much , but I don't have anything to base that assumption on. I'm getting rite at 2 zips dry per sq/f so I think I'm doing OK on yield. I think there is a lot to be learned yet on cob lighting. Hopefully my experience helps .

Sounds like a pretty similar situation then, I imagine mine starting show the symptoms farther away from the light since I was running at 50w/sqf. Good to know I'm not the only one experiencing this though, and it sounds like it is related to the light intensity a good deal.

KonopCh said:
As Cobkits said. I have 29-32°C in tent and my plants looks really good and happy. Just try to get as close to optimal VPD as you can.
And with that temp you can also fed more lightly because plants need more water than nutes.

Staying close to optimal vpd is somewhat of a struggle for me, since I am finding it extremely hard to add humidity back to the air. During the spring/fall it is easy with no heat/ac, but once the AC is on (house AC, not within the tent) I find it nearly impossible to add humidity back at a stable level. Any suggestions on this would definitely be appreciated!

HydoDan · Jun 17, 2017

hillbill said:
Do the symptoms occur on leaves that are close to the lights but not in direct light themselves?

Mine was like a slow burn that affected the whole plant.. Other plants only had slight burns at the top.. I am just now getting a couple crispy leaf tips.. Buds are ok but the worst affected didn't fill out like it should have..

VegasWinner · Jun 17, 2017

Sureshot2 said:
Hey all, so I built a COB fixture using 8x citi 1212 3500k 90cri's for my 4x2' tent. The lights at the time were being driven at ~50-52 watts each and the fixture has been roughly 10-12" from the canopy for most of the grow. At around week four or so I started noticing some rusty spots on the leaves directly under the lights, along with a small of amount of twisting/deforming. I initially thought this might be a cal or mag issue and increased the amount of calmag in my RO water to around 200ppm per gallon, but this didn't seem to help at all. By week 5 the rusty spots starting turning into leaf tips getting brown and crispy, eventually moving down the whole leaf, as well as many leaves starting to canoe on a different strain in the tent.

I have been told differing thoughts by various people, some saying it was a temperature/rh issue (VPD??), some saying the lights were too close/needed to be dimmed and others saying it was a lockout issue (I don't think this is the case). Before this grow I was using T5's using the exact same regimen/environment with no issues which is as follows:

3 site RWDC
pH ~5.7-6.1
PPM during veg ~550-600, flower ~650-750 (0.5 scale)
Nutes are GH Flora Duo + Calmag (using RO water)
Additives include Floralicious+, Mammoth P, KoolBloom (Liquid from weeks 3-7, dry from 8-9)
Res is non sterile using Heisenberg based tea
Temps on average are around 75-80f, RH is around 45-50%.
Res gets changed every 2 weeks.

After some suggestions from a friend I dimmed the lights from 50-52W per/sqft to around 40 during week 6, but obviously at this point damage was already done. There was also a point between week 2-4 where the temps were hitting 85-90 on some days due to some warm weather and AC being out of service. At this point I'm not worried about this crop since I'm already in week 8, but I'd like to narrow down what the exact problem was during this grow so I can avoid these issues on the next grow. It does seem like the damage hasn't gotten any worse after dimming the lights, but this could just be a coincidence?

Here's some pictures from a week or so ago:

View attachment 3962259 View attachment 3962261 View attachment 3962262 View attachment 3962260

Sorry if there's any information missing, I'm pretty tired right now. I can grab some more pictures if needed tonight.

Sounds like oxygen depravation which can occur if you are not keeping up with the nutrient regiment or roots to wet not getting enough air
namaste

Sureshot2 · Jun 17, 2017

VegasWinner said:
Sounds like oxygen depravation which can occur if you are not keeping up with the nutrient regiment or roots to wet not getting enough air
namaste

I'm running RDWC with around 1500 GPH of air over six buckets with 2 large stones at each site, plus water temps are chilled to around 66-67 so I don't think its an o2 issue. Roots are also snow white in color with no hints of slime or browning.

Here's some more recent photos I took today:

As you can see most of the foliage is perfectly fine just underneath the canopy where I moved some buds out of the way or along the side near the walls of the tent.

HydoDan · Jun 17, 2017

Your plants took a bigger hit than mine.. but now I know for sure it was too much light..
Hard one to diagnose... We're your fan leaves praying straight up?

Sureshot2 · Jun 17, 2017

HydoDan said:
Your plants took a bigger hit than mine.. but now I know for sure it was too much light..
Hard one to diagnose... We're your fan leaves praying straight up?

Yeah you're definitely right about the hard diagnosis, especially since the early symptoms looked like a deficiency and there was no apparent bleaching or anything. The leaves did starting pointing up and rolling inwards on the starfighter once things started getting bad, however the harlequin did not point up or really curl, those leaves just got crispy.

MMJ Dreaming 99 · Jun 17, 2017

Sureshot2 said:
I started running the Floralicious+ and Mammoth P based on recommendations from several other friends running hydro/rdwc since I'm running bennys and not a sterile res. The temp issues has since been addressed with AC and changing the lights on time to at night. I do think I'm going to drop the liquid koolbloom since I don't see it doing much and it causes the pH to go up.

This is what I figured, so hopefully turning the lights down to 40W/SF will be better? I had always been told to keep temps under 80f, should I be letting it climb higher? I'm adding about 2 gallons a day to my res with 3 plants growing.

One thing to consider in the future is adding o your mixsilica. It makes the plants stronger to handle temp variations.

Sureshot2 · Jun 17, 2017

MMJ Dreaming 99 said:
One thing to consider in the future is adding o your mixsilica. It makes the plants stronger to handle temp variations.

I always wondered about this since one of the guys at my local hydro shop who's actually pretty knowledgeable suggested I add this as well, but I kinda assumed it was snake oil without really looking it up. There seems to be a wide variety of products for silica supplements, I wouldn't mind something like ArmorSi or Silica Blast since these are only $30 a gallon at my store, but some of the other ones (name failing me right now) run like $70 for a pint. Which one do you use and at what rate?

Troubleshooting new COB grow

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