I have never seen this before turning solid black in veg. This is the sundae stallion. Yesterday was droopy. Today it looks 100 times better. But for some reason it's just two fans. I originally thought I was too hot on the soil mix. But now I'm not sure. It's only the two fans. On the samenose. Across from each other. It has black water?? Transpiring from the one. You can see the dot.
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If it was too hot all your tips would be burnt. That is indeed some pretty dark necrotic markings.
Curious why do you think the soil was too hot?
Any ideas of what certain nute you may have added too much of?
What is the pH of your soil run off?
I personally think given previous description you over watered that one bit much and it just locked something out for a bit.
Since the issue is on the lower oldest leaves I think you locked out a mobile nutrient. I think this was only temporary due to reason above.
By the way for anyone interested knowing mobile and immobile helps to diagnose things often.
Mobile nutrients are nitrogen in the form of nitrate, phosphorus (P) in the form of phosphate, potassium (K), magnesium (Mg), chlorine (Cl), zinc (Zn) and molybdene (Mo).
Calcium (Ca), sulfur (S), iron (Fe), boron (B) and copper (Cu) are immobile.