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Yellowing leaves... Possible Nitrogen N or Magnesium Mg Deficiency???


New Member
Hey all, hows it going everyone. Need some assistance with this grow.

They are having problems with lower and low middle leaves turning yellow. Old growth only.

They have been in FFOF for about 3 weeks, but they have been yellowing as soon as 10 days after transplant into OF. I had originally only been giving them Big Bloom at 1/2 strength with every watering, but later I read that RO water may need Cal Mag despite FFOF supposedly having it in there already. I have been giving 1ml/L GH Calimagic since the 20th of last month as recommended on the bottle. They have all received 3 waterings at this strength. The last watering included 1.75ml/L Pure Blend Pro Grow 3-2-4 on all my plants and the largest plant that is 5 days older received 3.5ml/L PBP. That plant showed what I thought to be signs of nute burn (yellowing of the tips and pointy edge things on the blades of the leaf) so I flushed with water.

I just got a pH meter last week and the pH runoff is showing a little low, around 6.1 or 6.2, and the nute solution I had fed with was way low, around 4 (and water started off at 6.3 before adding nutes) but that shouldn't matter if the runoff is above 6 right? Regardless I am now pH correcting everything I give them, last watering was CalMag only, pH adjusted to 7.1 to counteract the previous low pH feedings.

Don't know if this is a Mg or N deficiency as they both look the same to me and I have yet to see any high res comparison pics side by side.

My questions are as follows:

1) If its an N def then it must be a lockout issue right? (since they showed signs of nute burn when I gave more N; and since FFOF should not be N def. after less than 2 weeks)

2) Also I thought a pH of around 6.1 shouldn't necessarily be that bad and shouldn't cause lockouts...

3) If its a Mg deficiency then how long does it take to correct that? Is the 1ml/L enough or should I be using more?

And of course if its some other issue that I'm missing entirely please don't hesitate to tell me.

I really appreciate the help! Thanks in advance!

Pic #1 here is the one that's a week older that got slightly burned.

These next 8 are all the most recent:








These were when the first signs of yellowing was noticed on 9/17


And the first time I noticed yellowing between veins on 9/19

The full feeding record is as folows:

8/18 - Germ papertowel after soak 24H distilled water
8/20 - Plant in Lightwarrior in 9oz clear plastic cups
8/30 - 1/4 str FFBB
9/06 - 1.875 ml/L PBPg, 3.9 ml/L FFBB
9/10 - transplant to 1/2 gal FFOF 3:1 perlite
9/14 - water with 3.9 ml/L FFBB
9/17 - water with 3.9 ml/L FFBB
9/20 - water all with 1ml/L CaliMagic
9/26 - wilted due to underwater, water with 1mL/L CaMg, 7.5ml/L BB, 1.75ml/L PBPg,
one plant with double strength (3.5 ml/L PBPg) showed signs of burn
10/01 - water with CaMg 1.5ml/L, pH adjusted to 7.1

*one plant is a week older, but the rest of the plants were born on 8/18


How long has this problem been going on?
Happens on all plants after they reach a certain age.
What strain are you growing?
What was the establishing technique? (seed or clone?)
What is the age of your plants?
Planted germd sprouts on 8/20, transplanted to FFOF on 9/10
How long have they been in the soil mixture they are in now?
since 9/10
Were they in the same mixture when they were seedlings/smaller plant? If not, what mixture were they in before?
Germinated in lightwarrior. Might have kept them in there for a little too long and stunted them but when they went into OF they took off.
How Tall are the plants?
6-7 in maybe
What PHASE are the plants in?
What size pots are you using? (Include how many subjects to pot)
approx 1/2 gal
What substrate/medium are you using?
FFOF 3:1 with perlite
What brand Nutrient's are you using?
GH Calimagic, FF BigBloom, Botanicare PBP Grow
How much of each nutrient are you using with how much water?
see above
How often are you feeding?
no set regiment yet, trying to feel them out and correct this deficiency
What order are you mixing your nutrients?
calimagic > bigbloom > PBP
What is the TDS/EC/PPM of your nutrients used?
What is the pH of the "RUN-OFF"?
around 6.1, tested with electronic tester
How often are you testing pH/ppm/EC/TDS?
every time I feed now
How often are you watering?
~ every 4 days, when they get dry
When was your last feeding and how often are you feeding?
see above
What size bulb are you using?
8x 23W CFL 5000k and 6500k
How old is your bulbs?
What is the distance to the canopy?
What is your RH Factor? (Relative Humidity)
between 50-75%
What is the canopy temperature?
What is the current Air Flow? (cfm etc.)
6" fan blowing across plants
Is the grow substrate constantly wet or moist?
What water are you using?
RO (walmart drinking water in 1g jugs)
If using RO,Distilled,mineral water, what is the ppm/EC/TDS without any additives?
Are plant's infected with pest's?
No, killed maybe 5 gnats over the last month


New Member
Problems with Nitrogen being locked out by PH troubles.
Waterlogged soil and Soil with low organic matter.

Nitrogen is a very important element in the plant, all of them are but some are more important than others. For soil the best ph to have is 6.8. Why? Because at 6.8, that’s the best number for ALL available nutrients to be absorbed into the plant without any of them being locked out. For hydro and soil less mediums best ph to have is around 5.8.
Try not to keep your plants to cold, because the cold temps will cause the nitrogen harder for the plant to be absorbed.

PH levels for Nitrogen:

Soil levels
Nitrogen gets locked out of soil growing at ph levels of 4.0- 5.5.
Nitrogen is absorbed best in soil at a ph level of 6.0-8.0. ( wouldn’t recommend having a ph of over 7.0 in soil) best range to have nitrogen is a ph of 6-7. Anything out of that range will contribute to a nitrogen def.
Corrective Action
I would raise you PH to 6.8 and also I would double your CalMg nutes. Should correct itself it 1 -- 2 weeks. Also if you do have water logged soil, dont apply more water / nutes until top 2 inches of soil is dry.


New Member
The important part is the new growth coming out. From what I see in the pictures it is looking very green and healthy so whatever corrective action you have been taking it seems to be working.


New Member
Thanks lol

Yeah the soil is fine, it has 30% perlite and I always let it get dry between waterings, which takes about 3-4 days. If anything I am underwatering a bit; I am told this is better than overwatering because it causes the roots to expand more.

I was thinking it was Mg, because they have had plenty of Nitrogen from the OF and the nutes they had been getting, and only recently had they started getting Mg added (to RO water). Its impossible to tell a N deficiency and a Mg deficiency from the diagnosis picture sheets I have seen, at least in the early stage.

Is there something about these pics that tell you its N over Mg that is lacking?

I thought these were "mobile" nutrients so shouldn't they go back to the yellow leaves after the new growth has had its fill?

Thanks a lot!


New Member
Nitrogen deficiency will typically fade an entire fan leaf to the yellow shade at the same time, not the tips and or spots and patches.
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