I thought I had a K deficiency. Changed the water in RDWC 3 days ago with more K. Problem is spreading nevertheless. First 2 photos is same leaf, 3 days apart. It has spread to multiple plants by now.
the tank that feeds the RDWC is only 0.4 and has fed 60L into the system by now, so EC should have been dropping in the last 3 days. pH decreased from 6.3 to 5.9. So I know something is definitely wrong….