Please help: worrying leaf discoloration cause?

[Trogoliath]

Please help me in identifying this problem. I have wrecked my mind trying to find someone who faced similar issues... with no success yet.

This baby is almost 3 weeks old (since it sprouted from seed), and since my first application of nutes (measurements obtained from Botanicare's web calculator) the plant's growth was too fast for me to spot the cause of this faded discoloration on two of my (middle section?) leaves. The discoloration's territory is increasing by day and my paternal instincts are pleading with me to cut off those 2 leaves now to stop it.

However, the farmer within is too curious to blindly start ripping off leaves off his autoflower plant. I need to know what I'm dealing with here.

Funny thing is, I can only see the symptoms on only 2 of my mid-section leaves (with the top and bottom ones being fine as hell). This leads me to deduct it's not light/heat/wind burn. Also I can't recall seeing the discoloration before i started adding nutes/supplements to my RO water, but the plant is too young for me to have noticed anything really (this strain kinda grows fast).

I am worried that this could be one of those burrowing pests that leaves a trail on the leaf. But I have zero past experience with any pests (other than those little spider mite fkers that are not currently present).

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Strain: White Diesel Haze Autoflower (Sensi Seeds)
Current State: Veg (20 days from sprouting)
Medium: Soil (N: 200-500 mg/l) (P: 200-500 mg/l) (K: 300-600 mg/l) (PH 5-6)
Current Pot: Airpot 3 Gallon
Light: DiamondSeries DS200 LED hung at 2.5 ft from canopy (approx 75 cm)
Temp: 78 F (~ 26 C)
RH: 35-40% (cool mist humidifier using RO water)
Water: RO filtered water
Watering Cycle: using lift method (roughly once every other day)
Nutrients: Botanicare Pure Blend Pro Grow (2.5 ml per liter) + Cal_Mag (0.5 ml per liter) + Liquid Karma (0.5 ml per liter)
Misc Info: Semi-open Closet Grow. One oscillating fan (facing walls for gentle breeze effect)
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[Antics]

Your PH is far too low for soil.

You'll need to fix that before we can accurately diagnose the problem. You want to aim for a PH of 6.5.

 

[Trogoliath]

Antics, thanks for the chart I've never come across that before. I did a soil PH test today, and my soil is currently at the 6.0 mark. Tried looking for limestone to adjust the soil PH, but so far no luck (ordering online takes 2 weeks). However, during today's check-up on the plant I found that the leaf scarring turned from faded green to brownish-yellow overnight. Watered with half strength nutes, just in case.

Theory: Could this be cal-mag deficiency due to the soil PH? Would it be beneficial/advisable to increase my Cal-Mag supplement from 0.5 mg/ltr to say 0.85 mg/ltr... or is that just wishful thinking?

Gotta start preparing for worst-case scenarios. Can I continue growing using 6.0 PH soil (at the cost of a slightly decreased yield), or is it kinda doomed, unless I add dolomite lime?

I'd truly appreciate any kind of info at this time

 

[Antics]

I know it's not the thing people like to hear, and everyone hopes to just get that one answer from someone with tons of growing experience, where they say "oh you just have xxxx deficiency, add xxxxx and its fixed" but in this case we can't.

As the chart shows, some nutrients are only absorbed at certain PH levels. Like you see Nitrogen is absorbed from 6.0-7.0. Above or below that, and the plant isn't able to absorb as much. As the PH drops lower or higher than that, Nitrogen can end up being totally locked out.

Now when you look at Calcium and Magnesium, they can only be absorbed between 6.5- a little over 7.0.

So if you keep your soil PH at 6.3 all the time, your plant will be unable to absorb Calcium and Magnesium, or at the very least, can only absorb small inadequate amounts of it.

My soil likes to climb to a PH of about 7.5 naturally. So I PH my nutes and soil down to 5.5-6.0 depending on where it was before I feed, and then by the time my PH reaches 7.5 it's time to feed again. By doing this it allows my plant time to absorb throughout the entire range.

Now onto your plant, we know we have a low PH, and we see some problems. You could quite possibly have enough nutrients to feed the plant already in the soil, but due to a PH being outside of the range for those nutrients, we consider the plant to be locked out.

So we have 2 possible solutions. We can fix PH and see if that fixes the problem, or we can add nutrients. If we add nutrients without correcting the PH, we can end up with an abundance of nutes in our soil, which can easily cause nutrient burn. This only further damages, and stresses the plants. In extreme cases, this will kill your plant.

To properly diagnose most problems, the PH needs to be stable, and within range.

You can grow with your soil, but it will require continued maintenance, or will require the addition of something to buffer at a slightly higher PH. You'll find some more helpful information about PH (and everything else) in the link in my sig: Everything You Need To Grow Cannabis

 

[Mike Wright]

I think Antics has it nailed. I can tell you from experience if you add calmag you will actually make the problem worse.

 

[Antics]

I think Antics has it nailed. I can tell you from experience if you add calmag you will actually make the problem worse.

Just add to what you've said so we have everything covered, Cal Mag DOES work great wonders for Cannabis, but only when it's added when it is needed. Otherwise excess Calcium and Magnesium can lock out more nutrients, as seen in this chart:

Trogoliath, don't forget about the link in my signature: Everything You Need To Grow Cannabis
That link is a collection of all growing topics that will help you grow the best plants you possibly can.

 

[Trogoliath]

So we have 2 possible solutions. We can fix PH and see if that fixes the problem, or we can add nutrients. If we add nutrients without correcting the PH, we can end up with an abundance of nutes in our soil, which can easily cause nutrient burn. This only further damages, and stresses the plants. In extreme cases, this will kill your plant.
Cannabis

This is exactly what I'm experiencing now (just after my 2nd watering cycle). Nute burn symptoms developed, so i'm backing off on them chemicals for the time being.

Thank you Antics for the great info. I'm very familiar with the link you shared, but it's always good to read up more.

Thanks again guys. My next step is to monitor the plant and water it (without nutes) until I get my hands on some lime for the PH adjustment.

 

[Antics]

I unfortunately can't help with using amendments to adjust the buffered PH, as I haven't done any of that yet myself, I can only point you back to the PH topics in the 'Everything youu need to grow Cannabis" topic.

I currently use PH down from General Hydroponics to PH my water and nutes. You could do something similar using PH up, if you chose that route. I use the dry powder opposed to the liquid product.

 

[Pbass]

Cal/Mag/PH as stated. It's gonna get worse looking, don't worry about it it'll grow right past it. I use 2tb vinegar in every gallon of water I serve. It brings my ph down from about 7.8 to 6.5. That benefit dissapates pretty quick though, so you can't premix too far in advance. That's ok for me, I never mix until it's gonna be poured on something right then.

This lil guy turned out fine.