It greatly depends on the nutrients you are using since Calmag usually is Calcium Nitrate that means has substantial N in it 4-0-0 for some 1-0-0 for other Cal supplements if you were using a N rich formula as a base like many Micro products you would steer clear of 4-0-0 as it would increase N
Some product lines like GH have 1-0-0 Cal mag which would be fine for use for first 3-4 weeks of flower during stretch and initial bloom but in soil much of what you use remains stored in media and degrading perilite will naturally release Cal over time since it is important for nutrient transport and structure it is never entirely removed but most micro B in 2 part systems have lots and your plant is no longer producing foliage or stems so only trace amounts are needed for mobility.
It’s addition during flower can be summed up as using 1 thing means less I can add of another since ppm only allows for so much at anytime without burn which is non reversible and has tragic effects in flower. Also knowing that the majority of plants growth has ended (not supporting new foliage) it’s demands are far less meaning it builds up in soil and plays havoc with ph if your ladies do not want or use it. [quote=“Paranorman, post:1, topic:8967”]
I always use it otherwise my leaves turn yellow and eventually fall off !?
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that is caused mostly by the decreased N and your plant canabalizing to get more Macro nutrients but if using Cal helps by all means I am only voicing what I have found works for me. I cut Cal mag out once stretch is done with no ill effect of note get less tip burn and easier flush