yellowish leaves

Hello, Im on 5th week of flowering. It started on second week of flowering. It begins like this: the plant starting from the top becoming pale green until all the plant become pale green then fan leaves become yellow, plant stems and leaf stems turn red. Leaves start to die plant stunts. I...

First grow, one of the plants has yellowish leaves, still green but a slight tint. The leaves are also curled down a bit. What could cause this other than overwatering as I don't think I am overwatering and other plants seem fine? Many thanks Sarah x