Sorry dude but that makes no sense at all. Cal mag breaks down salt deposits? Where did you get that info? Flushing with cal mag? That's one of the worst ideas I've ever heard of. Most cal mags contain nitrogen, which is something that should be scaled back if not totally eliminated weeks before flush.
More importantly though, flushing is for eliminating elements from your medium so the plant is not up taking the chemicals (fertilizers) that we don't want to be smoking. So by pouring a shit load of water (I prefer RO) through your medium (mine is coco) you will be reducing the total ppm of accumulated fertilizers each flush day. Coco holds onto
calmag big time, so reducing it half way through flower and eliminating it soon after is a good way to make flushing easier.
Don't believe the BS, "you should never just give a plant straight RO water." I go straight RO for 2 weeks with no PHing and my plants look fine through it all. The only thing that you will notice is leaf yellowing after the first week or so. This is what we want. This indicates the plant is starving for nitrogen. Which in turn means we did a good job flushing, and our nugs are going to smoke clean and pure.