I'll let someone with more coco experience weigh in here, I grow in 35% coco 35% potting compost 10% perlite and 20% organic amendments.
This may help:
http://growersguidetocannabis.com/a-guide-to-growing-cannabis-in-coco-and-perlite/
This may help:
http://growersguidetocannabis.com/a-guide-to-growing-cannabis-in-coco-and-perlite/