Why this happens? Leaves turning dark to yellow

Soil isn't buffering. Ph drift over time. Generalized uptake problems. Harvest is slready suffering.

Potassium and calcium deficiencies. Probably also hungry for phosphorous.

Greetings, it's clear that your plant had an immediate physiological reaction to a change in the root environment. Osmotic Shock, the sudden darkening of the leaves after watering indicates osmotic shock due to excess nitrogen or salts. When applying fertilizers to a substrate that might have been too dry, the plant absorbed the nutrients through mass flow violently. That petroleum green color is a warning that the plant became saturated with nitrogen, which led to a collapse in the transport of other nutrients. Magnesium Blockage (Interveinal Chlorosis) The yellowing you observe with the green veins is an induced deficiency of Magnesium (Mg). It's not that the nutrient isn't in your BioBizz product, but it can't enter the plant for two reasons: Potassium Antagonism: In week 4, excess Potassium (K) blocks the entry of Magnesium. Salt Accumulation: Even if your output EC is low, there may be a "bio-accumulation" in the roots that prevents the absorption of microelements. The Critical Factor: pH Meter Calibration For this diagnosis to be accurate, it is mandatory to know when the last calibration of your pH meter was performed. If the device has not been calibrated with buffer solutions (4.0 and 7.0) for more than 15 days, the reading of 6.25 that you see is incorrect. A deviation of just 0.3 or 0.5 points in pH completely blocks the absorption of Iron, Magnesium, and Zinc. Without recent calibration, we cannot trust that the plant is receiving what you measure. Other Influencing Factors Solution Temperature: If the watering water was very cold (below 18°C), phosphorus absorption stops immediately. Root Hypoxia: If the watering was too heavy after a prolonged drought, the roots were left without air for a moment, causing the stress that ended up in yellow leaves. Suggested Action Plan Immediate Calibration: Before the next watering, calibrate your meter. If you notice that the reading was off, there we have the culprit. Stabilization Watering: Perform a watering only with water at pH 6.2 (adjusted with the already calibrated meter) to help "clean" the excess salts and rebalance the substrate. Gradual Dosage: In the next feeding, use 50% of the usual dose to allow the plant to recover its transpiration rhythm without becoming saturated again.

hi ....that looks like a cal-mag deficiency to me....... Add cal-mag to the watering water and water it every time with...... After 2-3 waterings, it should get better...... Good luck

Massive oxygen deprivation. Most likely oversaturated medium. Anaerobic fermentation will skew pH to boot. Organic nutrients will require you to feed the rhizosphere as well as the plant. Oxygen travels 10,000 times slower in soil than air. Oxygen travels 320,000 times slower in saturated soil beyond a point. Microorganisms scavenge Oxygen in direct competition with the plant. Even if you think your medium is airy it may well be but a Oxygen lockout rapidly breaks down nearly every process over time as aerobic is switched for anaerobic. Soon as a medium gets soggy iron becomes unattainable causing yellowing as Rubisco cannot regenerate chlorophyll. Everything else is a symptom of the breakdown in oxidative phosphorylation and atp production and the resulting ph skewing as more and more lactic acid is pumped into medium due to lack of oxygen. No atp, no nothing.

Your plants needed nitrogen during the stretch and now they need cal mag for building buds and if it doesn't have it, it will take it from the leaves

After having a look to your diary, you have found the 2 main problems, first was overwatering and second was too intense light. Those 2 problems leads to Magnesium deficiency. When stems and petioles leaves start to turn purple it’s the earliest sign that tells you there’s a lack of magnesium. Magnesium is the central ion, bound by 4 Nitrogen atoms in the photosynthesis molecule. Magnesium gets used up at first during the photosynthesis process. It is crucial for light absorption, particularly the bleu and red wavelengths. This is why purple starts to reflects from the thinnest walls cells of the plant like leaves petioles and leaves stems when there’s a lack. Adding too intense light have lead to a photoinhibition on top of the overwatering problem. The last problem is the cultivar, autoflowering plants don’t forgive any mistakes during their life cycle. Any mistakes will have repercussions on the final yield.

Hey Buddy let’s start by saying this plainly, but gently: 👉 You didn’t ruin anything. 👉 The plant is talking early, that’s good. 👉 This can be corrected. Now let’s read the plant honestly. ⸻ 🌿 What the plant is telling us From the photos + timing: • Widespread yellowing (not just lower leaves) • Yellowing between veins in places • Leaves were dark → then yellowed fast after feeding • Week 4 flower (this is key) This is not normal fade. This is not senescence. This is a nutrient uptake issue, not lack of nutrients in the bottle. ⸻ 🔍 The core problem (very likely) This looks like a lockout / imbalance, not simple deficiency. Most probable causes (stacked): 1️⃣ pH drift in the root zone • Input 6.2–6.5 is fine • But BioBizz + organics can drift the medium fast 2️⃣ Nitrogen & Magnesium not being taken up • Especially common in early–mid flower • Explains interveinal yellowing + fast color loss 3️⃣ Feeding strength vs plant demand mismatch • Dark leaves → sudden yellow = uptake disruption Runoff EC being lower than input tells us: 👉 nutrients are not staying available, not that there’s too much. ⸻ 🚨 Why this matters in week 4 Week 4 is: • Bud-building phase • High N + Mg demand • Still very vegetative internally If this continues unchecked: • Bud size suffers • Plant cannibalizes itself too early So yes in my humble opinion adjustments are needed now, not later. ⸻ ✅ What I would humbly suggest (step by step) 1️⃣ Reset gently (don’t flush aggressively) • One watering with: • Corrected pH (aim 6.3) • Very light nutrients • Goal: stabilize the root zone, not strip it 2️⃣ Re-balance nutrition • Make sure Nitrogen is still present (BioBizz Grow doesn’t disappear in flower) • Add Magnesium support if not already (very common with BioBizz) 3️⃣ Stop chasing charts This is important: 📉 Charts are averages. 🌱 Plants are individuals. Feed the plant, not the paper. ⸻ ❌ What not to do • Don’t increase EC blindly • Don’t wait “to see if it fixes itself” • Don’t assume this is normal flower fade At week 4, yellow = signal, not style. ⸻ The buds are still forming. The plant still has time. Correcting this now will show improvement within 5–7 days. Leaves that are already yellow won’t turn green again, that’s okay. What matters is new growth stabilizing. ⸻ Bottom line (humble, honest) You’re not far off, but right now the plant is underfed functionally, even if bottles say otherwise. Check: • Root-zone pH • Nitrogen presence • Magnesium availability Do that calmly, and she’ll come back into balance , growers love my friend and please remember this is just my humble opinion , always follow your instinct 💚

Might be that your girl has used all the goodstuff in your substrare and needs a re charge. This has happened to me before. The biobizz organic feeds work in tandem with the soil. If the soil is depleted your girl will show signs of deficiencies. I up potted mine to 5 gall pots with fresh substrate as I still had around 6 weeks of flowering till harvest. After which I continued to add nutes in water as per schedule. This corrected most deficiencies after a week or so. Previously effected leaves will still show deficiencies but new growth will appear healthy. Other than that you have a good grow going. Best of luck man.