The general rule I have found on here is to start using nutes after 5 weeks at low end (if not half of low end) potency.

CalMag may be different though, I have a feeling that can be used a little earlier.

Fill out the trouble shooting form that is a sticky in the main "plant problem" forum. You will get much more help if you have that as it answers a lot of the ....what if..... questions.