3rd week of flowering, mid-top fading

Hi guys I’ve posted about this last time and can’t seem to figure out what is causing this. I have some Trilogy OG under 3 1000 de lamps, and some under a HLG 550 led. It seems to happen every time I hit this point in flower at three weeks just as I defoliate. So I pick all the yellowing leaves off and kinda forget about and it turns out decent. But I’d like to figure this out maybe with you guys help. The lights are kinda close just like every other time about 18”. The plants are in 5 gal and get fed like 4 times a day when the lights are on. I’m feeding a modified Lucas formula of 4micro 10 bloom in flower. I have temps and humidity under control. I do drop the micro from 6 to 4 at flip just wondering if this looks like they need more nitrogen. I also started GH Floralicious at .5 and Kool bloom at 1ml. Total feed is about 650-750 runoff is close to that. I use calmag maybe once a week if I remember. Could the lights cause stress like this even if my temps are in line? It actually seems like the plants under the led have it worse but it could be just the different spectrum playing tricks on me. Anyway I also have c02 at 1000ppm. I know that’s a lot of random info but hopefully you guys can’t help be nail this. Thanks