potassium deficiency?

Your plants show signs of nutrient deficiency, and from what I see, potassium deficiency is a strong possibility. The symptoms of yellowing edges and necrotic (burnt-looking) tips, are classic for potassium (K) deficiency. Here’s how to diagnose and fix it but let's start from. 1...Possible Causes soo.. 1. Potassium Deficiency: Leaf edges burn and curl up. Yellowing starts from the tips inward. Overall slow growth and weak stems. 2. Magnesium Deficiency: If it were magnesium (Mg), you’d see interveinal yellowing (yellow between the veins, but veins stay green). It’s common in coco if you’re not supplementing Cal-Mag. 3. Salt Buildup / Lockout: pH (6.0) is within range for coco, but a salt buildup could cause lockout. EC 1.2 is slightly low for mid-veg to early bloom in coco. You might need to increase it. How to Fix It 1. Increase Potassium (K) Supply Use a PK booster (e.g Plagron Green Sensation or Big Bud from week 2-3 of bloom). You could also try a potassium sulfate supplement if you want a quick fix. 2. Check Your Calcium-Magnesium Balance If you haven’t already, use Cal-Mag at 0.3-0.5 EC before adding other nutrients. Coco tends to retain calcium and magnesium, so it’s important. 3. Increase EC to Around 1.5-1.8 (Slowly) Coco drains well, so plants can handle higher feeding compared to soil. If your runoff EC is way higher than 1.2, it means salt buildup → flush first. 4. Ensure Proper Drainage & No Salt Buildup Run 20-30% runoff when watering to prevent lockout. Immediate Steps: Feed with a bloom formula that includes higher potassium (K). Add Cal-Mag if you haven’t already (especially in coco) Happy growing ! And if I was helpful feel free to hit me a like 👍 and if you need more Info you can always send me a PM.

Wrong NPK ratio or overfeeding, could be very low ph, but then spread would be around all plant.

Burning from over feeding.

Not sure what deficiency she might have but you said coco coir medium you need to use a nutrient line specifically made for coco coir. I just started using coco coir. My grow supply store hooked me up with Canna Nutrients for coco A & B and pk 13/14 during flower. Might be worth looking into.

If you said you did not buffer the coir before and then did buffer it right, that would be an abundance of Ca and K. and should not need any more. But the old growth will not fix or riper it is stuck like that. The new growth should be better as its all corrected now. The ec of 1.2 seems a bit high IMO but some plants can take it. plus it should have the required nutrients in it. Hard to say when we don't know what it is. Might be best for you to start a diary so other can see whats going on and when,

That looks like classic nutrient deficiency but I don't know what you're feeding it. Can you elaborate?