i don't think you mentioned ph in your post. go get a ph meter and correct your water / nutes before you water. 6.3 going in. I keep hearing to not stress about what it is coming out.

I doubt the Cal Mag has anything to do w/it as long as you are 10ml/G or less or your water is really hard to begin with.

next time use sunshine mix or fox farms instead of the pre-fert stuff as that's harder to control.