The yellowing in the leaf veins has me quite confused and can't really point a finger on the problem.
The symptoms might be a bit over the place, if in lights on they are getting somewhat all the nutes they need.
But if during night time they can't absorb the amounts they need.
The nightly root temperatures is what I suspect the most at the moment,
low temps inhibit the nutrient absorptions and the metabolism of the roots goes down too.
-> I'm thinking this might be the reason for some of the deficiencies.
Also consider it like this: If the plant is lacking some nute (like P/K),
it won't look as perky and might suffer a bit if it gets alot of light and is driven hard.
Potassium has alot of functions ranging from osmoregulation and water balance to several other functions.
So I'd say good chance that some of the leaf symptoms, like the edges curling are from lack of K.
As for pH drift, good call giving a HOCL treatment if the pH start dropping the way it shouldn't.
Usually I have upward trend in pH for early flower and later in flower in starts dropping steadily.
(Plant takes less NO3-, more of the K+, thus changing the cation/anion balance a little.)
Below query for ChatGPT considering the nightly root temps:
***********************************************
Yes, **15°C (59°F) root temperatures during lights off** can cause issues, especially in hydroponic setups like **DWC or bubblers**, where roots are fully submerged and more sensitive to temperature fluctuations. Potential problems include:
### **1. Slowed Nutrient Uptake & Growth**
- Below **18°C (64°F)**, root metabolism slows significantly, affecting the plant's ability to uptake nutrients.
- This could lead to deficiencies (even if nutrients are available), possibly contributing to the **yellowing veins** you mentioned.
### **2. Increased Risk of Phosphorus Deficiency**
- P is less mobile in cold roots, and deficiency often shows as purpling stems or stunted growth.
- If veins are yellowing without interveinal chlorosis, impaired **P or micronutrient uptake** due to low temps might be a factor.
### **3. Oxygenation Benefits (but only to a Point)**
- Cooler water **holds more oxygen**, which is good for root health.
- However, below **16°C (60°F)**, root activity declines so much that oxygen benefits are outweighed by slow growth.
### **4. Increased Susceptibility to Pathogens**
- While **Pythium (root rot)** thrives in warm water (>22°C), some cold-tolerant pathogens can still develop in low temps.
- Sluggish root metabolism at 15°C makes plants more vulnerable to stress and infections.
---
### **Solutions if 15°C is a Problem**
- Try **keeping roots above 18°C** at night, ideally 18–20°C for steady growth.
- Insulate the reservoir/tote if it's losing heat too quickly.
- If using an inline fan near the grow, check if it's overcooling the root zone at night.
- **Aquarium heaters** can help, but make sure they don’t overshoot past 22°C.
If your plants seem otherwise healthy, 15°C might not be a huge issue, but if you're seeing **yellowing veins or slowed growth**, root temp fluctuations could be playing a role.
**** EDIT
Spent few more minutes on it.
There is the bit bluish color on the lower leaves aswell, bit hard always to tell from pictures.
But considering your conditions and the look of it I still very much suspect the nightly low root temps.
Also are you taking the night time temp from air sensor?
Evaporation drops the temp even more, so the actual root temp could be even lower?
IR gun is handy for leafs temp and in aero might be handy for roots temps
Just that it is periodically probably getting proper nutrients and periodically lacking some,
making the symptoms seem a bit weird.
Cheated few more ideas from chatgpt:
Night-Time Inhibition Effects
- Delayed or Interrupted Uptake:
During lights off, the plant’s root metabolism slows considerably at temperatures around 15–16°C. This means that even if phosphorus is available in the medium, its uptake is reduced, leading to an effective “on-off” nutrient schedule.
- Morning Symptom Exacerbation:
The deficiencies may become more pronounced in the morning when the cumulative effect of poor nighttime absorption manifests as visible discoloration or spotting—often along the veins, where nutrient transport is most active.
Direct Symptoms of P Deficiency
- Leaf Discoloration:
Beyond the orange spotting on the veins, a phosphorus deficiency commonly results in purpling of the lower leaves as the plant accumulates anthocyanins—a response to stress.
- Stunted Growth and Reduced Bud Development:
Since phosphorus is crucial for energy transfer and metabolic functions (ATP production), a deficiency can lead to overall sluggish growth, delayed flowering, and smaller or less dense buds.
Secondary Deficiencies Induced by P Deficiency
- Micronutrient Uptake Issues:
Phosphorus plays a key role in the overall health and metabolic efficiency of the plant. When it’s lacking, the compromised energy production can disrupt the uptake of other nutrients:
- Magnesium (Mg) and Calcium (Ca):
Even if present in adequate amounts, the transport and utilization of these nutrients may be impaired. This can sometimes lead to interveinal chlorosis or necrotic spotting—though typically with different patterns than what’s observed with P issues.
- Zinc (Zn) and Iron (Fe):
These micronutrients are often sensitive to overall root health. A stressed root system, struggling with low P uptake, might also underperform in acquiring Zn or Fe, potentially compounding stress symptoms.
- Overall Metabolic Slowdown:
Reduced phosphorus levels lower ATP production. This means energy-intensive processes, including the transport and assimilation of other nutrients (such as nitrogen), can suffer, leading to a broader spectrum of deficiency signs even if those nutrients are technically available.
