There are 2 situations when I use calmag. Whenever I use ro water, I use botanicare calmag+ at 5ml per gallon.
The other time is after I have ensure my ph is correct and ec in range, I will add calmag+ if the plants are telling me they need it.
If your source water is tap with a ppm over 150, you should be ok ditching the calmag. I do not use calmag in my tap water grows. My tap water is 300ppm alone.