Brown spots on leaves

First signs of a potassium deficiency. Easily solved by adding a P/K booster to your line up, or upping the dosage if already using one.

Low K - the distinctive progression around the serated tips. Barring ph or nute lockout, raise your levels of K a bit while minimizing effect on other nutrients. See if that clears up the interveinal chlorosis too. If it's slowly progressing, always better to tackle one thing at a time unless absolutely certain.

https://420life.com/wp-content/uploads/2021/10/Marijuana-Leaf-Deficiency-Chart-scaled.jpg This is a leaf chat to help diagnose the issue. I don't know if I agree its to much P, no diary so no idea what your feeding them. But a few things can cause the symptoms. Most notability is a lack in K. Could also be a lock out but again no real idea. need a diary and more info. Check your EC and PH if you can. help elimate some of the common trouble shooting steps.

Curling tips and browning edges, too much phosphorus...go easy on the nutrition 'cause you are just begging the flowering. Try to correct doing a couple of waterings with some kelp solution (Ascophyllum nodosum) mixed with water to correct the nutrition excess and after that use in just one day, some Cal/Mag and everything's going to be fine at last. Keep the good work. 420.