Help guys! What is wrong this time? Is it the high...

Your EC is likely too high based on what I see . If you are feeding with Calmag and your still showing signs of cal mag problems its because your feeding too much and its resulting in a lock out preventing your plant from absorbing nutrients it needs . Your on the right path for the feeding schedule by not feeding it with nutrients every single time but I would add one more PH corrected watering in between the nurtrient watering's so it looks like : water , water , nutrient water , water ,water nutrient water and so on . This will do a few things for your firstly it will allow your medium to be "flushed" removing all the salts from your root zone enabling the plant to start absorbing nutrients again secondly it will make your plant absorb most of whats in the medium before you add new nutrients to the medium preventing lock outs like you have now as well as nutrient burns . Once you do this I would suggest adding 2ML / L of Calmag to your nutrient solution and resume the feeding programme . Your leaves will slow down on the yellowing and come back to that nice lush green we all know and love . The leaves that are really damaged will NOT come back to normal I advise you trim these leaves away to prevent any unwanted pests from coming to make themselves a nice home . I also find that your PH range is abit low for a soiless set up I would try and have it around 6.0 but as it looks its working for you BUT this may also be the cause of the lock outs as well , PH plays an important part in nutrient uptake for your plants so I always advise going in the ranges that the medium you are using calls for in your case (6.0 - 6.3) a hydroponics system will have it set at (5.5 - 5.8) and a soil set up will be at (6.5 - 6.8) I hope this information helps shed some light into your grow and gives you the information required to get your plants back to rocking and rolling. -Happy Growing!