dead leaves

Details This is my first grow. I use a large LED grow light, growing in coco coir, and feed them Fox Farm "Grow Big" liquid plant food (See contents in the image attached). I feed them filtered water and add nutrients every other watering. I water them every 2-3 days when the coir is mostly...

Can someone please tell me what this is and why it’s happening ? Useing fox farms nutes tiger bloom and beastie bloom. Under 4 quantum board 132. How can I save them ? Thank you for your time Sincerely 3000 Ps I have some ideas on what it might be and have some basic knowledge.