I've had a Magnesium deficiency using LED's and Light-Mix / BioBizz nutes, but I suspect it's because I, until recently, neglected to check the pH of the run-off - I watered with pH 6.50 and the run-off was a whopping 7,89 so the Mg might have been locked out somehow, also my tap water has a lot of calcium in it
I add 2 ml/L of Canna Mono Mg with every watering, but I'll lower it as the pH stabilizes.
I didn't have Mg def last grow when I was using HID light, but then I was also measuring my pH with the colouring drops and aimed for max 6.0.
So if you stay on top of the pH and don't see red stems, white tips and leaves yellowing between veins your likely in a decent range, but it's a good idea to have some Ca and Mg or CalMag on hand if you need it.
My most Mg def plant (White Widow - Dinafem)
A nice little chart
Happy growing