Help me identify my problem. It’s happening to the 3 largest plants out of 6 (all different strains)

hey Buddy , so What I’m seeing (from the photos) Key visual clues: • Rusty/orange necrotic spotting across fan leaves • Burnt serration edges (“crispy teeth”) • Damage is older leaves first, not new growth • Buds look healthy and frosty, pistils normal • LED-grown, mid–late flower This is not pests and not disease. And it’s not cold stress either (cold gives purpling and limp tissue, not this). Primary diagnosis (most likely) ⚠️ Potassium (K) deficiency with secondary Magnesium (Mg) lockout This is a classic flower-stage LED symptom combo. Why this fits perfectly: • K deficiency = edge burn + rust spots • Shows first on fan leaves in flower • Very common under high LED intensity • Gets worse if: • EC is a bit low for flower • Root-zone pH drifts • Ca-heavy feeds block Mg/K uptake Why LEDs make this worse LEDs increase: • Transpiration efficiency • Potassium demand (stomata regulation) • Magnesium demand (chlorophyll + enzyme activity) So a feed that worked fine under HPS often becomes insufficient under LEDs. This is super common — nothing “wrong” with the way you growing. Just to be very clear: • ❌ Not calcium deficiency (no twisted new growth) • ❌ Not nutrient burn (damage pattern is wrong) • ❌ Not pests (spots are necrotic, not stippling) • ❌ Not wind burn (distribution is uniform, not directional) (action plan) 1️⃣ Check root-zone pH • Soil: 6.2–6.5 • Coco: 5.8–6.0 Even a small drift can lock K & Mg out. 2️⃣ Increase K availability Depending on their nutrient line: • Boost bloom base slightly OR • Add a PK booster lightly (not aggressive) ⚠️ No crazy PK bombs — this is correction, not force-feeding. 3️⃣ Add Magnesium • Epsom salt: 0.3–0.5 g/L (once or twice) • Or Cal-Mag low Ca / higher Mg ratio This often stops the spotting within days. 4️⃣ Lower light stress slightly • Raise LEDs 5–10 cm OR • Reduce intensity 5–10% This reduces K demand immediately. 5️⃣ Do NOT chase damaged leaves • Those leaves will not heal • Focus on stopping progression • New damage stopping = problem solved Timeline expectation • 2–4 days: spotting slows • 5–7 days: no new edge burn • Bud quality remains unaffected Honestly? This plant will still finish strong if corrected now. This looks like potassium deficiency with magnesium lockout, very common under LEDs in flower. Check pH, slightly increase bloom nutrition, add a bit of Mg, and reduce light intensity a touch. Damaged leaves won’t recover, but you’re just aiming to stop it spreading. You got this Buddy lets grow and keep us posted 😊 Growers Love 👊👊👊