Calmag is overused. If you're using tap water and a soil like Fox Farms you don't need it at all. Excess calcium can lockup multiple nutrients making them unavailable to the plant.
You only need to use something like calmag if you have a calcium or magnesium deficiency. But if you have either one of those deficiencies there are better solutions than calmag. If you have a calcium deficiency treat the plant for that. The same with magnesium. But most of what people identify as a deficiency is caused from too much of something making what the plant is deficient in unavailable.
How the hell did calmag become something every new grower just fed their plants? Some are feeding calmag from day 1. It does more harm than good.