Ca issue...double check the amounts you're feeding, how often, etc. The problem with 'calmag' solutions is that if you only need Ca, you're still adding Mg. Sometimes our plants only need one or the other and adding that which we don't need causes us issues. I would re-study my nutrients and reassure myself I'm giving the plants what they need as a whole, then, if I felt I was still short on Ca, I would add it by itself.
Note: If you're allowing the coco to dry out, you're hurting yourself and the plant. Also, don't use plain water, ever...in the type of grow you're attempting. Always use a feed solution, even if it's weak (ie 25%)...but never just plain water.
