Here's my system -- it works great for me as I've never had any burn issues or deficiencies with it. I grow in DWC.
What I use: AN 3-part system and Cal/Mag. I mix up a liter of it according to directions, but I don't use it that way. Since I've got a ppm meter, I start with a res of plain water and then add small amounts of my mix, stirring up the res, until I hit these numbers:
Seedling 1-2 weeks old - plain water
At around 2.5 or 3 weeks, I add enough of the mix to bring ppms up to 300
4 weeks, 400
5 weeks, 500
6 weeks, 600
7 weeks, 700
8 weeks, 800 (this ends up being roughly 1/3 strength of what's on the label)
When I switch to flowering, I keep it at 800 to the "end"
The "end" isn't the end of flowering, it's whenever the plant stops taking nutes. This happens around week 5 or 6 with most of my grows. They stop taking nutes and start pulling energy from the fan leaves. Then I just watch the ppms
at some point the ppms start rising because they're drinking water but not absorbing the nutes. So I stop adding at that point.
The reason I add Cal/Mag is my water's natural ppms are low -- about 50. So I end up with a deficiency if I don't add a bit.
That's it, couldn't be simpler.