COBs and deficiencies - Any correlation?

Dear growers,

I'm currently running my first grow with COBs. I noticed the appearance of deficiencies that I didn't had before, Magnesium being the most noticeable.
I have been struggling to fix it, first checked my pH, seemed a bit low, added some dolomite. Later, added some epson salts, things improved a bit.
However, one day I went to check my plants and dimmed the lights, then forgot to turn full blast again. Next day when I went to check they were looking healthier and the foliage more vigorous than ever. So, I would say the lights are having an impact on how defiencies progress in my grow.

Now, thing is, in theory I guess I'm not providing too much light. I have 5 citizen 1212 4000K, totals 250W, in a growing area of 0.42m2 which correspond to 1260 PPFD. Lights are placed 10"-12" above the canopy, don't think I have signs of light bleaching.

(Plants are growing in soil, 4th week flowering, 3 gallon pots)

Is this only me, or some of you have also came across the same issues after switching to cobs?

Not sure if I should simply dim the lights or try to fix the problem other way around.

Dim it down, seems way overpowered...
I have been recommended 200w setup for a growspace about .75 sqm

What lights were you using before? 1260 PPFD is very high in the scheme of things, so the soil and roots would have to be very on point to keep up. I flower 3'-4' ladies at about 750 PPFD, but I have to lollipop them a bit to avoid larf when they are 4' tall.

The great Supra himself! Glad to see ya!

I have had similar experiences, the high intensity light just brings the plant requirements so much higher in general. Took me about 3 cycles to adjust to the new lights. I run no till pots so it's not like I can just up my PPM. I even notice that my habits as a no till grower a much more aggressive compared to friends and other people on IG growing no till. I have to top dress frequently to keep up.

I could just dim...but what is the fun in that!?

Considering the thread "tomate" posted, it seems many COB users had to increase cal/mag feed in order to the keep up with the higher PPFD.

SupraSPL said:

What lights were you using before? 1260 PPFD is very high in the scheme of things, so the soil and roots would have to be very on point to keep up. I flower 3'-4' ladies at about 750 PPFD, but I have to lollipop them a bit to avoid larf when they are 4' tall.

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I used mainly cheap LED lights before, my bet is the PPFD was much inferior.
My plants are 2' tall in 3 gallon pots, so I would say they aren't the most resilient and strong plants. I will follow your suggestion and dim a bit.
How did you end with that number (750 PPFD)? Trial and error?

At this PPFD levels you probably need to raise the CO2 concentration and keep the room at >= 85F.

PPFD around 800 to 1000 max is what you want w/o extra CO2.

Running 73F at soil level, 78F at canopy level, no extra CO2.
You are right, photosynthesis is optimal at higher temperatures, which I don't have.
Just dimmed my lights from 250W to 170W (1260 PPFD to 860 PPFD). Took to long to fix the problem, at 4th week, bud formation is already compromised...

Glad this problem was reported before, (shame on me didn't find it). Thanks for your help.

Metacanna said:

I used mainly cheap LED lights before, my bet is the PPFD was much inferior.
My plants are 2' tall in 3 gallon pots, so I would say they aren't the most resilient and strong plants. I will follow your suggestion and dim a bit. How did you end with that number (750 PPFD)? Trial and error?

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Yes that makes sense, the cheapo LEDs make a lot more heat than light LOL. I settled on 750 PPFD as a compromise for my ideal bud size and based this chart, adapted by @Rahz, I marked the area I settled on as a compromise between efficiency and yield/sq ft. Most growers would put more emphasis on yield/sq ft so maybe 900 PPFD.

That's great info. Based on that graph, assuming we are using COBs, I would say above 600 PPFD one would need to spend around 60% more energy to get 25% more yield. Not counting the risk of something going wrong when growing conditions are pushed that hard.

I have a mix of Nanolux DE and home built cxa3070 AD bin led's. At 170 watts the led were burning the plants and at first I didn't know what was going on. To me, the LED even at cxa3070 are on the same level as the NanoluxDE and I'm right around half the watts per sqft as the HPS. I lifted and dimmed the lights and in a few days things started looking better. I also did add cal mag from General hydroponics.

IMO pull the lights away or dim, see if that helps over a few days and then bring back down as stuff gets green again. I did this and this is my Strawberry OG day 53 despite the burn around the 2 week mark into flower.

That's the same intensity I was using. One cab 730 and the other 770 PPFD. I was pulling between 52 and 58 g/sqft which I think is pretty good. The lamps I currently offer are designed to provide mid 900s PPFD but with people pushing the levels recently I've struggled deciding whether to follow the trend.

SupraSPL said:

Yes that makes sense, the cheapo LEDs make a lot more heat than light LOL. I settled on 750 PPFD as a compromise based on my ideal bud size and also this chart, adapted by @Rahz, I marked the zone I settled on as a compromise between efficiency and yield/sq ft. I suspect most growers would put more emphasis on yield/sq ft so maybe 900 PPFD.
View attachment 3936791

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Rahz said:

That's the same intensity I was using. One cab 730 and the other 770 PPFD. I was pulling between 52 and 58 g/sqft which I think is pretty good. The lamps I currently offer are designed to provide mid 900s PPFD but with people pushing the levels recently I've struggled deciding whether to follow the trend.

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Personally, I love your lights and may eventually order more, once this goes through:

http://www.inquisitr.com/4083695/tulsi-gabbard-introduces-bipartisan-bill-to-decriminalize-marijuana-federally/

I'm pretty happy with the end product at this point and have gotten a lot of complements and repeat buyers. However, the T series I currently produce won't be around for much longer due to the time/work involved in fabricating and assembling them. I have a couple things in the works... I have some partially assembled lamps on the way. I'll still be the one buttering the cobs and wiring the DC circuit. Price per watt will be similar to the current offering. I am also working on DIY kits but not wanting to reveal too much at the moment.

Rahz said:

I'm pretty happy with the end product at this point and have gotten a lot of complements and repeat buyers. However, the T series I currently produce won't be around for much longer due to the time/work involved in fabricating and assembling them. I have a couple things in the works... I have some partially assembled lamps on the way. I'll still be the one buttering the cobs and wiring the DC circuit. Price per watt will be similar to the current offering. I am also working on DIY kits but not wanting to reveal too much at the moment.

Click to expand...

Definitely will keep my eyes open for where you take it next.