Soil stores excess nutrients whereas a DWC or coco grow the nutrients are on demand. It's the main reason why you see changes so quicky in hydro type grows.
When you have an excess amount of Ca and Mg you start to lockout other nutrients such as P and K. Many users find themselves giving more MC because the plant looks healthy. In soil the plant only uses what it wants at the time. Then all of a sudden in flower the plant demands more K but it can't get it becasue of the excess Ca and Mg.
The chart below looks confusing but once you start to understand it things will make sense.
So when I hear of people having to add Calmag and they are using MC as well the first thing I want to know is that they are following the calculator's max dosage and not going over that. If you feed high amounts of P and K to the plant, which we know MC is high in, then you start to lockout Ca and Mg. By doing a quick rinse of the soil and coming back with a lower amount of nutrients the problems correct themselves.
Growers using MC see the Ca and Mg def and naturally add more calmag.
