I would be careful about pre-charging your coco with cal-mag. If you have enough cal-mag in your nutrient formula, you can cause an abundance and end up locking out other nutrients by using extra cal-mag in your initial rinse. H3AD's formula, if used with Epsom, does not need pre-charged coco, and pre-charging it can cause issues. Settle on a nutrient feeding, and then decided if you want to pre-charge your coco or not.
That said, invest in a damn good PH meter. I have seen so many growers buy $120 worth of seeds, but an $8 PH meter, then have deficiencies, not realizing they simply locked something out. Calibrate it every damn feeding if you have to.