Flushing

Lets start with flushing- flushing is done by using either tap or distilled water (with distilled being more effective hence used less), you run about 50-100% (depends on how saline your soil is and what water you use to flush) of the pot volume in water/distilled water to dissolve any excess salts in your soil down to the runoff. As for over-watering you can avoid it completely by making sure your plant has proper drainage, and that after every irrigation the runoff will be about 30% of the volume watered. About nutrients, I'd suggest dropping the Cal-mag for now since plants rarely need high amounts of that in their grow cycles. Increase the macro nutrient (N-P-K) amount in irrigations (about 1/4 of what is suggested as seedling, 1/2 during veg, and full dosage when flowering) if any deficiencies appear then increase the fertilizer responsible. Now lets go back to flushing, you have no reason to flush right now since your plants are showing signs of deficiency, heck a flush would actually make it worse. As suggested try increasing fertilization without the Cal-mag and check if it helps. If that doesn't help try checking the pH levels of your irrigation, acidity might cause macro-nutrient deficiencies. Good luck with your grow! Happy growing :)