What could this be?

Sick Plants & Problems
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Where was the coco sourced? Was it bricked? Was it prewashed by manufacturer? Unwashed coco has a tendency to be like a magnet for cal mag that will soak em up and not give it up to the plant, a good coco company will wash their coco with cal mag to create that buffer zone. Something to maybe consider? I don’t grow in coco but listened to a bit of grow talks on the subject and one bit of info that stood out to me