Hey. This is my 2nd grow using a hydro top feed method. Plants have been healthy throughout the veg cycle and I started flowering about a week ago. Just changed the reservoir yesterday and today one single leaf is showing signs of some type of deficiency. I am growing Gold Leaf which is a 60/40 indica hybrid that grows like a sativa (real tall). The problematic leaf is a large fan leaf near the top of the plant and also pretty close to the light. I have ruled out light burn because there are a few higher leaves that look healthy.
pH was about 6.1 when I changed the rez and now has fallen to about 5.9. PPM is a bit high at 1800 so I am adding some pH’d water to bring it down. The leaf is showing clear signs of yellowing (bright) between the veins. Although the leaf is high up, it is not new growth because it is already a very large fan leaf. That is making the forensics harder for me. What is weird is that only this single leaf is showing these symptoms all others look relatively healthy.
My initial thoughts: iron deficiency or magnanese deficiency.
Any help would be appreciated.