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.

Saludos está claro que su planta tuvo una reacción fisiológica inmediata a un cambio en el entorno radicular. Choque Osmótico, el oscurecimiento súbito de las hojas tras el riego indica un choque osmótico por exceso de nitrógeno o sales. Al aplicar fertilizantes en un sustrato que quizás estaba muy seco, la planta absorbió los nutrientes por flujo de masa de forma violenta. Ese color verde petróleo es el aviso de que la planta se saturó de nitrógeno, lo que derivó en un colapso del transporte de otros nutrientes. Bloqueo de Magnesio (Clorosis Intervénal) El amarillamiento que observa con las venas verdes es una deficiencia inducida de Magnesio (Mg). No es que el nutriente no esté en su producto BioBizz, sino que no puede entrar a la planta por dos razones: Antagonismo por Potasio: En la semana 4, el exceso de Potasio (K) bloquea la entrada del Magnesio. Acumulación de sales: Aunque su CE de salida sea baja, puede haber una "bio-acumulación" en las raíces que impide la absorción de microelementos. El Factor Crítico: Calibración del Medidor de pH Para que este diagnóstico sea preciso, es obligatorio saber cuándo se realizó la última calibración de su medidor de pH. Si el aparato tiene más de 15 días sin calibrarse con soluciones buffer (4.0 y 7.0), la lectura de 6.25 que usted ve es errónea. Un desfase de apenas 0.3 o 0.5 puntos en el pH bloquea por completo la absorción de Hierro, Magnesio y Zinc. Sin una calibración reciente, no podemos confiar en que la planta esté recibiendo lo que usted mide. Otros Factores de Influencia Temperatura de la Solución: Si el agua de riego estaba muy fría (menor a 18°C), se detiene la absorción de fósforo de inmediato. Hipoxia Radicular: Si el riego fue muy pesado tras una sequía prolongada, las raíces se quedaron sin aire por un momento, causando el estrés que terminó en las hojas amarillas. Plan de Acción Sugerido Calibración Inmediata: Antes del próximo riego, calibre su medidor. Si nota que la lectura estaba movida, ahí tenemos al culpable. Riego de Estabilización: Realice un riego solo con agua a pH 6.2 (ajustado con el medidor ya calibrado) para ayudar a "limpiar" el exceso de sales y reequilibrar el sustrato. Dosificación Gradual: En el siguiente abonado, utilice el 50% de la dosis habitual para permitir que la planta recupere su ritmo de transpiración sin saturarse de nuevo.

hi ....das sieht mir nach cal-mag Mangel aus....... Gib zu dem Giesswasser Cal Mag zu und giesse es jedesmal mit...... Nach 2-3 mal Giessen dürfte es besser werden...... Viel Glück

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.