Plant turning yellow and leaf turning brown spots

Well a review of your diary I do see a few things. So in coco coir I see you’re watering at 6.4 PH. In vegetation you kind of want to be in the 5.5-6.0. 5.8-5.9 is a good place to be. Your plant also seems to lack a little nitrogen, so it’s time to drop the rooting stimulation nutrients and introduce some “grow” feed. Potassium is more for the flowering stage so I disagree with TheRollingStoned420. I also think you may need to up the calmag a bit as I suspect that this deficiency is causing your leaves to rust a little. So when I mix nutrients I put calmag in first and I want to be at around 250-300 PPM on the .5 scale of the digital TDS meter. Then I add all the rest of my nutrients after the calmag. So I think if you tray and get a bit more dialled in you should be on your way to helping your plant do better. Cheers 🤙