Calmag issues? Rust spots.

You have nutrient lockout from a salt buildup in your medium. Stick with just PH water until you get your PPM's back to around 100 less of what you feel they need( My guess is 800ppm so water until 700). Then start with 800PPM and see what your runoff is. When feeding you want to always keep your PPM's in within 100 of PPM going out or you will start to get a buildup. I would not do a drastic flush all at once as it can cause more harm then good(**Unless you see a drastic decline in health). A flush over time should be all you need to get back on track. It will most likely take a week or more to get things back to normal numbers and a few weeks to stop seeing symptom's. You will notice when you near harvest she almost stop's eating and your required ppm's will drop dramatically. Good luck and Happy Growing