As already mentioned here, high heat/feed.
Those deep red stems and brown patching on leaves could point to P lockout. Aswell as the dark green of the leaf, losing color could point to late stage N-tox.
Nearly always due to FFOF being a preloaded hot soil and not properly accounted for when given feeds.
Pics would deffo help the folks here diagnose the severity of these problems and will go along way in getting you the fix ya need!