Deficiency?

P excess and Ca lockout flush ASAP then feed anew with 200-250ppm

Buy some Cal mag if you dont have any and a Ph meter and Ph up and down. Make sure you are also Phing you water to 6.5 PH. if you are using nutrients mix everything first make sure to use CalMag and Ph to 6.5 Before feeding!!

Calcium deficiency often shows up as those dry, crispy brown spots on the lower leaves – just like on your plant. Young plants in a fast growth phase need plenty of calcium, especially if you're using reverse osmosis (RO) water or very soft tap water, and growing in coco, light-mix, or anything with high drainage. When calcium deficiency is combined with a lack of magnesium (a common issue), you start seeing stuff like rusty patches, yellowing between veins, and even parts of the leaf tissue dying off – which is exactly what seems to be happening here. So yeah, this really looks like a classic CalMag deficiency, possibly made worse by pH issues or soft water. Fixing it with a proper CalMag supplement and keeping an eye on pH should help a lot. Here's what you can doing/checking: pH check: For soil, I'm keeping the water between pH 6.2–6.5 to make sure nutrients are actually available. Water quality: If you're using RO water, CalMag is a must. For tap water: if EC is below 0.3 mS, it's too soft – again, you’ll need CalMag. Feeding : Not going overboard. Just using 1/4 to 1/2 strength nutrients for young plants until they get more established.