..keep your Ca input up bro',... recall, coco's odd CEC properties make it a Ca hog, and will bind it strongly to itself, beating out the roots for it, until it's sated, then the Ca is released more readily,... Ca uptake in coco is better at 5.8 or a bit below, relatively speaking, so to treat your defc., running a bit more acidic for a while can help,..I'd say this is just a plain lack-of type defc., so up that dosage, mate!