Your clawing and overfeeding issues comes from using "Calmag" on top of a A+B coir base that already containing it.
Next time follow basic recommendations for coir. If you add more minerals in this case Nitrogen, Calcium and Magnesium coming from "Calmag" on top of a already calculated and optimal mineral ratio intended for coir you will as a result destroy that optimal ratio and experience nutrient toxicities and lockouts from overfeeding.
PK13/14 will also worsen it, Cannabis need low to moderate levels of phosphorous and excess levels of K is very detrimental for potency. It has no place growing in containers and will only give you problems. The plant need a complete plant food from start to finish at different concentrations. You realize that different feeding schedules and products are mostly a result of marketing when the mineral ratio should stay the same throughout the grow.
Flushing with plain water is the worst thing you can do in coir! Use a light EC and pH corrected solution if you really need to flush!
Hope that helps and happy New Years!
Cheers!