Causes of brown leaf spots

Overall plant health is good! Just started to develop these spots a couple weeks ago. Thought it might be nutrient lock out because of high pH, but corrected that. I have been adding foxfarm cal/mag about once a week at 1 teaspoon per gallon. Starting to think it could be a rust fungus. Took off all affected leave and removed from area. If left, the slowly yellow and get worse. So not a rapid mover this. But it seems rust fungus usually happens at flower. Im still vegging
Granddaddy purple photo.
Indoor tent average temp 75, rh is 52ish plenty of fans. 4 fans from the top as part of my lights and an oscillating fan from the side.

If it wipes off with fingers its not rust mold @Rockdog62

And is that the only leave that’s like that my friend happy growing

Unfortunately not the only one. Dozens more.

Did it wipe off by rubbing it between fingers to see if its mold

Doesn’t seem to rub off. This thing got really dense! Trying to thin her out some while keeping the photon collection machine working full tilt lol.

What nutrient line are you using? Dosage? Could be simple as a deficiency.

Using bergmans nutes. Running close to directions at about 2/3 teaspoon per gallon once a week. Tried to go a little light at first.
From the pic you posted potassium is the most likely. however if that were true I’d suspect nutrient lockout. Last i checked soil pH it was 6.1 ,down from 7.4 after a flush. I’ll check today after the coffee kicks in lol

Doesn’t seem to affect new growth, or prefer old growth, just random leaves.
I’ve cut all affected leaves off. Needed a trim anyway. Ill wait to see what comes back. I guess it’s entirely possible that this WAS nutrient lock out and i just missed some leaves lol.

Wow you’d think this was my child or something! Except with my kid i had more than a few short months to figure it out! The urgency with which these grow makes for an exciting ride! I told my wife, that even if I didn’t smoke it, I’d still want to grow!


As I’m looking at these I don’t see much for potassium. I happen to have some RAW potassium from my last grow. The seedling mix has the most and I barely used it because the soil was already loaded.

Going through and cleaning, changing batteries on pH and ppm meters. All bluelab stuff.

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Sounds like you have it figured out bud. I’ll tell you this, coco is way easier to grow in. You don’t have overwatering issues and you feed daily. I went the Jack’s 321 route in coco and it’s been smooth sailing, with great results. Just food for thought on next go round.

Thanks @Highwayman420 I’ll look into growing in coco! I’m intrigued! But this is my second grow and I’m just now “feeling “ the soil lol!
I don’t know much about it but I’m guessing it’s kind of a crossover between hydro and dirt? I like the idea of knowing exactly what nutrients are there! I never know when to start feeding! Washing through as an infant to test ppm doesn’t seem smart . Yet i have seedling nutes that i can almost never use because of loaded soil lol

Coco is treated like a hyro grow. Coco is a neutral medium and very forgiving. Just make sure you have the time to dedicate to watering. My flowering girls are taking a gallon per day, per plant. But overall, growing in coco is so much easier…for real.