I thought I would chime in m my two cents just to offer a different opinion.
I am an organic grower and I don't like any synthetic substance in my plants. In fact the main reason I started growing is because I didn't want to smoke chemicals.
Some will say that an adequate flush will rid the plant of any remaining chemical nutrients, but my belief is different.
Years ago women weightlifters were spoon fed steroids(chem nutes) to make them successful at competitions like the Olympics. After they passed competing age they stopped using steroids(flush), but these steroids had dramatically altered these women and after they tried to go back to looking like women the after effects were obvious.
you can see that here
My solution to the problem of cal mag feeding is simple. when preparing my soil mix I wash dry and crush 2 eggshells into powder and add them to the soil. egg shell is 100% calcium so that takes care of half the problem. for the mag I use molasses in the feeds.
No disrespect to the chemical nutrient lovers out there, each to their own. I just prefer to use methods where the results and after effects are proven and documented. The methods I use have been used for hundreds of years.
There is a new chemical everyday and nobody knows the long term effects of ingesting or smoking plants altered with these chemicals.