ppm meter is another way to test your nutes.
if ppm rises in your runoff decrease your nute strength
if ppm falls in your runoff increase strength.
you should get to a point where your ppm decreases slightly coming out thats where the plants are feeding happily.
Also make sure with coco that you feed everytime you water , the odd plain water day is ok, then towards harvest day start using plain pH6 water for 7-14 days.
J