What is your nutrient solution strength? Im thinking your going into nute lockout, I use the Flora nova grow and use way, way less than recommended. You might also have high pH in your soil. Do you use any cal/mag? I would recommend a heavy flush with about half strength cal/mag added in. Flush until your EC is reading about 1.0 at run off and then start of with very lite feedings. I would also chop off anything that has turned yellow, it wont fix itself and go green again. Also, make sure you pH your flush solution, I would say 6.4 going in and check your run off pH.What goes in should be close to what drains out. That should get you back on track, dont flip until you have this fixed, you'll get a better yield if you wait.