i dont use any cal mag. i use tap water because our tap water here is pretty clean you can easily drink it. to me tap water tastes better then the shit i buy at the store with the added iron and stuff in it. if i don't use tap water i use rain water. we never run out of it. i been debating on using cal mag just as a precaution but my plants so far don't show any signs of cal/mag deficencies. the closest i got to it were on my current flowering plants that i induced nitrogen toxicity to which im pretty sure led to nutrient lockout.I have found it works (for me) to just add extra cal-mag on feedings, then nothing on the watering's in between.
I use my nutes (FF brand) at 50-75%, but the calmag always at 100%, and from about week 4 of veg until I start starving her at the end I use an extra 3-5ml/gallon.
i've asked others if i should add it but they all recommended that i don't unless im using RO water thus why i advised the same. by all means am i no pro just my 2cents.