I'm using a hydro grow with a 300W LED light. Things were going well until a week or two ago, and I was going to put them into the flowering stage, when some of the top leaves began to get yellow / black spots. I dumped out the nutrients and gave them a fresh batch and I thought the problem had been solved, but now many of my top leaves are yellowing around the edges and curling upwards. I'm at a loss as to what the problem is, my pH levels seem fine, and the temperature stays between 70-80. Is it possible that it's light burn / something else?
Looks like Ph problems causing manganese and phosphorus lockout, you said Ph seems fine but what range exactly?