So whats the deal with CalMag? (Jerry Seinfeld voice)

So the plant needs a source of calcium and magnesium. I think some peoples water supply has a decent amount of these minerals naturally, if you don’t or use RO, you need a good source of it. Base nutrients should contain some cal & mag. For instance GH micro has 5% calcium already. You run into problems also with coco that naturally absorbs these nutrients if not properly buffered.. so you end up needing supplemental calmag. Look at your base nutrients and see if there is a decent amount of calcium and magnesium in them.. I usually run a few mL a gallon regardless in veg and early bloom..