Always start with basics. Make sure your pH and EC are good going in and coming out. They look a little burned so your soil might be holding onto too many nutes. Your feed looks superconcentrated so even a tiny bit off on your measurements could be a big difference. Get an EC meter and test the ppms. You should probably be between 600-900ppms at this point. I bet you're registering over 1000 on in your runoff.
Assuming you have EC under control, I would look to calmag. It's really the only thing you might be missing.
Last possibility is a fungus. From the pictures, it looks like it could be, but I don't think that's the case here.