Nute burn or def?
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Burnz, looks like Phosphourous and/or Clacium deficiency to me. The leaf stems are red, which makes me lean toward P def. I also notice some leaf edges curling. How's your airflow, is this one closer to lights with less airflow....possible heat pocket? Obviously wait for Waira Wait for the real dealio.
What's the best fix for P def?
Plenty of airflow man, got 3 fans in the tent moving air. and the lights can barley move any higher. Lol.
Looks to be the beginnings of Ca def to me. I see you are in early flower, now is the time to up your CaMg and start P/K booster.
I might be locked out.. I'm giving 8-10ml/gal of CaMg for feedings and still has not fixed the problem.. I'm also use Floranova Bloom. 4-8-7.
Do you have a soil pH probe like an Accurate 8? You need to determine your medium pH. Use the Run-off Method if you have no other option. https://www.autoflower.org/threads/...-for-run-off-testing-and-ph-estimation.41733/ We really need some more info to be able to give any specific advice. Fill out this form, then copy and paste back here. https://www.autoflower.org/threads/...ill-out-first-with-the-data-that-matta.45991/ I use GH CaliMagic brand and grow under LED and use RO water. Many times I have to go as high as 3 ml/L or 12 ml/G. Many times you will not see improvement in your current symptoms, you just want it to stop spreading to new leaves.
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Burn'-- just how close are the lights? ... and overly strong air movement, a combined with low RH/high T, can cause stress with transpiration/cooling.. if it's bad enough, the stomata close up to halt major water loss, and this shuts down the flow of nute's as well, causing a localized defc. sometimes,... the high intensity makes for more Ca demand too.... Symptoms do look more P than Ca defc. but there's some overlap in the appearance sometimes, and I see some spotting hugging the mid-rib, a common Ca defc. symptom... And indeed, an overly low medium pH can lock out P, but we need an in-pot pH to determine that,.. like HM says, last resort is the run-off method, usually sucky for accuracy, but there's an improved method in this section, listed at the top as a Sticky (highlighted threads).. check that out,.... the deal is, if it's off pH, adding more will make matters worse, and if not, and it's a simple lack-of defc. holding off an further additions will also make matters worse!
...so the key here is to get that in-pot pH,...
And indeed, an overly low medium pH can lock out P, but we need an in-pot pH to determine that,.. like HM says, last resort is the run-off method, usually sucky for accuracy, but there's an improved method in this section, listed at the top as a Sticky (highlighted threads).. check that out,.... the deal is, if it's off pH, adding more will make matters worse, and if not, and it's a simple lack-of defc. holding off an further additions will also make matters worse!
Soil pH coming in at 7.5 ... I pH my feeds to 5.8
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Hmmmm... did you do the test in that thread, or take a quick measurement of straight run-off? Collected in something clean? 7.5 is hinting at possible excess of something that's forcing the pH up (CaCO3 inputs),... what's your water source, pH and if you have it, ppm/EC? And what soil is this (lime source)? If it really is over 7.0 in-pot, then likely sources of CaCO3 inputs besides the heavy Ca-Mg is the water, if it's hard; too much is just as bad! And with your feeds going in at 5.8 (normally that's too low), It gets to be a tangle here mate,.. potentially, too much Mg will block out Ca, but doesn't affect P uptake,... too much Ca can block K uptake, but no sign of that,... if the symptoms are actually P defc. there is a small window of alkaline pH that starts locking up P---> 
now you see why that Accurate 8 soil pH probe is such a valuable tool! With that, we can be more certain of the pH, and narrow things down some, and a ppm reading of the run-off would help a lot too,.... as you see, Ca is difficult to lock out with pH..
View attachment 736742......
The 7.5 was using a soil probe, and I know it's pretty accurate... I have not measured runoff yet because I watered a couple days ago.. I think I may have to flush her, but I don't want to do that just yet if I don't have too. But she's getting worse by the day.
I use tap water, that sits for atleast 24+ hours before I use it. It measures in at 7.0-7.5 before I put nutes in. That it drops to about 5.0-5.2 and I pH up to 5.8-5.9
Problem: possibly P defc
Medium/grow method: roots organic + biobizz light + lime
Feed: and supplements used: Floranova Grow + bloom, Silica Blast, Floralicious, CaMg 0-0-0, Kool Bloom
water source: Tap Water that sits out for 24+ hours before being used.
Strain/age: Frisian Dew 35 days old
light used: (2) Amare se450 uvb
Climate: 77-81 degrees .. 40-50% humidity
Additional info: I'm growing 7 other plants which seem to be doing just fine, they're not perfect but healthy and lush. I have a feeling this Frisian is locked out. Unless she really needs more CaMg? I could always up it to like 15ml/Gal ?
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