I've been curious what your position is on flushing. Thanks for sharing that, I fully agree.Calcium is rarely strain dependent. Pure sativas don't like a heavy EC. If you have a Kush for example that is a heavy feeder, just raise your base fertilizer a bit. Cal-Mag is a band-aid to sell you more stuff at the hydro store.
If your plants are burning, always water until 10-25% runoff. Test your pH going into the feed and coming out to diagnose any problems.
Length of flush depends on the CEC of your growing medium. You can flush rockwool for a couple irrigations and get a nice fade. Coco, maybe a week and a half or two. Heavily amended soil gives a nice fade when the plant is done.
Something ill add that I've noticed in a couple crops using peat based media, is if I wait too long to begin the flush, the uptake of water into the plant slows down so much at the end that getting a good fade can be difficult.
Now I keep a very close eye on water uptake in weeks 7 and 8 to get a feel for when to switch to plain water. As soon as she starts slowing down drinking I make the switch. Mind you I use rockwool now but I use the same monitoring process, and usually flush for about 5-7 days. Bit longer than necessary for wool, but not harmful.