Yellow leaves

At this moment I don't have picture of the plant because of bad lightning. I'll add it later if needed
But the problem is that big fan leaves are yellowing and so are some of the smaller leaves at the tops. Some of the lower leaves have also dropped. Could it be nitrogen defiency? I have been feeding them with Metrop CalGreen but it's not helping them at all. It's an indoor soil growth. water every 2-3 days and flush every 2 weeks (big plant in 14 liter air pot) run off water Ph 6.5 --- Ec 0.5 - 0.9
it's soon 4th week of flowering. Other symptoms: Only very few leaves looks like Eagle claw and rest is fine. Those yellowing fan leaves are at the top and approximately 40cm away from light source(400w HPS)
Leaves that are not getting so much light looks very good. no light green but "normal" to my eye
Strain info: Ed Rosenthal super bud and it looks like sativa domninant phenotype

I'm having the same problem with mine yellowing leafs turning chrisp at the tip mine as considered still seedlings Im guessing it's nitrogen deficiency so I fed them some but doesn't seem to be changing any but I've seen alot on here that if it's flowering and doing that they say it's normal because the plants coming to the end of its life so maby that?

When I see yellowing leaves in my mother room I increase the watering but keep the NPK the same in the res.