Yellow leaves. Low nitrogen or magnesium?

Need some help from some of you seasoned growers. Northernlights auto from ILGM. Found a few yellow leaves today. She was showing some signs of mild Nute burn, tips yellow but she has progressed into something a bit more so could use a little advice from more experienced growers. Not on all leaves just the bigger older fan leaves. The rest of the plant looks healthy otherwise. I’m thinking nitrogen with possibly magnesium deficiency. I’ve looked at the deficiency chart but there are so many similar images hard for me to really say . Pics included.

Strain; Type, Bag seed, or NA = Northernlights Auto ILGM

Soil in pots, Hydroponic, or Coco?= FFOF soil

System type?= Prescription blend nutrients

PH of runoff or solution in reservoir?= PH6.8

What is strength of nutrient mix? EC, or TDS=PPM in 860,PPM out 1470

Indoor or Outdoor=Indoor

Light system, size?+Budgetled 250r-spec+Meiju 240 r-spec

Temps; Day, Night = 82-84* day,66-68* night

Humidity; Day, Night=40-50%

Ventilation system; Yes, No, Size =yes Vivosun 6" exhaust with 18" Vivosun carbon filter

AC, Humidifier, De-humidifier,= no

Co2; Yes, No= no

How’s the rest of the plant look? Just in old fan leaves new growth too? You still in veg?

PH of runoff or solution in reservoir?= PH6.8

How much runoff you getting? Enough so there’s no salt build up?

Epsom salt and 3% hydrogen peroxide are good with (cleaning the wounds) if you wanna read up on those.

You could try brining her down to 6.5-6.3

Like you said a lot of issues all look the same so all we can do is continue to ask and eliminate what it is not till we know what it is.

Hope that helps

@ValiumZ may have a thought

Thanks. Enough runoff to almost fill the catch tray. 5 gal fabric pot. Getting 5ml of cal mag with each feeding/watering. Nutrients every other watering. Rest of plant is fine. She did get two half feedings of FFtrio before switching nutrient lines. Hoping next feeding might get her back in line. She looks fine other than a few yellow leaves which I removed today when watering. Tent did get up to 86* this morning but doubt that’s part of the issue. Typical high temp for tent is 84*.

Looks like a magnesium deficiency caused by lockout. Not sure how a plant responds to changing nutrient lines. I flushed mine and they bounced back. But there are far better eyes here for such things @Hellraiser @Bulldognuts
86 is fairly high I wouldn’t want to be ant higher than 80 max. Anything above 80 is considered bad in flowering imho. And when it is hotter plants will drink more. The big 3 is ventilation, temperatures and humidity. Never underestimate the importance of those 3. How often do you water? The leaves look droopy.


I don’t like to change nutes mid-grow, can do strange things, I’d continue feedling and maybe some calmag as well.


Thanks! Your recommendation was my gut feeling. Haven’t fed it enough of the FFtrio to really be an issue as far as lockout. Two feedings at 50% recommended amount. Have been doing 5ml of CalMag per gal per watering for both of the ones I have growing right now. One his Kind soil and this one is FFOF. I know the temps seem high but it’s what I have to work with. Pretty sure cannabis is still ok up to around 88* not that I would ever try to grow at that temp. Thanks to everyone for your input truly appreciated.

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Your runoff TDS is not out of line for being in FFOF but shows it’s nearly depleted. You have a magnesium def so time to supplement with cal mag.

Feeding the plant at around 800 ppm and monitor runoff; if it climbs then run water only until runoff drops back down.

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Ffof has nutes in it so if you gave it more this could be the cause. Generally I wait a few weeks depending on the plant size. Try to let soil exhaust its built in supply before adding more. At higher temps during flowering you run the risk of all sorts of problems, Plants will drink alot when its hot. Absolutely cannabis can survive in those temps but they do not thrive either. How are you venting the air inside out? All I am saying is your inviting more probs and lower yields, lower quality terpene profiles(vital for so many reasons) running above 80 degrees. Stale hot air is gonna teach you a lesson no grower wants to learn other than from others mistakes.

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@ValiumZ this shows soil is mostly depleted and needs to be supplemented the rest of the way to harvest. Viable OF would be more like 3,000 ppm.


At that ppm I would think it was fine for another watering. But it is why I am here to learn. My bluesky organics was at 7k was still feeding with a ppm at 1k so I naturally believed his was still loaded for a water or two. Stand corrected.

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I’m just relaying what we’ve been seeing as a general with OF. It’s all good. I am not up on much of the current nutrient lines and am more gravitating toward using Jack’s 3-2-1 and Autopots.

But I’m old and lazy.

Any information I do not know or is wrong and is corrected is always appreciated. I have personally never used FFOF only FFHF. Bluesky organics was something I had to settle on as I couldn’t find one store in my city that had a bag of FFOF it was all sold out. So my experience was limited really. I learned something.

Awesome! Thanks so much for the info! I also was thinking the same. Second time growing, first time using nutrients

I almost fed her again today but watered instead. Thinking feed her next two waterings?

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That’s what I would do.

So… instead of waiting for the next water cycle I decided to just go ahead and feed my NL plant. I figured it’s probably not much different than giving a flush. The feeding helped quite a bit she’s getting her green color back and perked right up after the feeding. I’ll just let her dry out good and do a second feeding when it’s time to water again. Does this sound like the right course of action? Thanks.

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