I think part of the problem is you're treating the coco like true soil, and that will always come back to bite your ass,... coco is a very specialized medium, far different from soil, with a lot of do's and don't's, much of it related to it's odd CEC properties (cation exchange capacity).... have you done your homework on coco? It's closer to hydro in many ways,... Are you reusing the coco? Do you monitor your EC/TDS (ppm's) going in and coming out? Are you ever just adding water alone (a no-no)? Are you running at least 15% run-off each time you feed, and testing both pH and ppm's of that run-off? Again, what brand of coco? ...problem is what you describe as the issue could be caused by several things,....