Newbie grower here. I'm growing in coco, so Cal-Mag is my religion, lol. It's like Frank's Red Hot Sauce; i put that shit on everything . I'm using GH Flora Trio, plus Armor Si and CaliMagiC regularly, at about 60% recommended levels.
I'm also doing just two plants with Fox Farm trio + Terpinator. No Cal-Mag for these ---but, if they become deficient I won't deny them. Also using these at about 60%. So far, 5 weeks in, just started flower, and the FF fed plants show NO need for cal-mag whatsoever. Oh and yes these are still in coco as well, i use Tupur, pre-prepared and buffered with perlite added.