how are ya? from what i have heard coco is pretty much a hydro medium so it wont actually have much nutes in it to begin with asuming what is also in the soil mix has. plant that size i would confidently give 1\4 strength nutes.
dont know how much help that was. btw you could check out this log it was done in coco with white widows


http://boards.cannabis.com/grow-log/...ized-coco.html