Do you use cal Mag through the whole grow
If you are watering with distilled or RO (reverse osmosis) water then it is highly recommended. Minimum amounts should do fine unless a deficiency is noticed. Reason being 0 or near 0 ppm water has no elements. Some prefer it to control every aspect of the plants growth. But in that case they definitely add cal mag in intervals the entire grow. My plants are mostly outside so i use rain water. Seems to do the trick for me but maybe im just extremely lucky
Cal mag with nitrogen should be avoided during flower, especially the last 3-4 weeks.
I know earth juice makes a product called oilycann which does not contain nitrogen. There are probably others.