6.8 might be too high for Coco... Can't speak from experience, but I've been looking into using coco in my future grows. I'd go and read up on what other people using coco are ph'ing at. Some say in the high 5's or low 6's, others say between 6 and 7 (6.5 best)... Maybe try adjusting the ph.

It would be a shame to throw away all of that coco. Why not get the Canna Coco nutes? Many people recommend it.