Watering every day in coco?

Coco retains calcium and magnesium to the point of saturation then gives it back up to the liquid at an inopportune time. This is well-documented. Early suppliers of coco required you to wash it as it retained salt water and needed to be rinsed.

You will find numerous references to flushing coco throughout the grow to reduce salt buildup. I personally see the runoff rise to levels above my input solution which would point to this:

Which is demonstrably NOT the case. I water to 15 to 20% runoff and use moderate concentrations of GH Flora line: yesterday in late flower 710 ppm.

Early suppliers of coco did not rinse it well, so users had to rinse out all the salts by flushing it well with fresh water. Do you think maybe you see concentrations of Ca and Mg higher than you feed because some of your feed solution evaporated and some went into transpiration? Both of those would leave higher concentrations of salts behind in the coco. That’s why you feed to excess. The concentrations equilibrate with your feed solution as it passes through the coco. The first bit will have a higher concentration. The last bit will not. If it doesn’t drop to what you are putting in, you didn’t put enough in. That’s the whole point of of feeding to excess.