spliff, some of this advice sounds pretty bunk.
You don't need to go buy cal/mag or put epsom salt in there either.
When mixing your res you can add 10 or 20% tap water to the mix.
Your nute levels are low for that size plant. I run low ppm myself, but I go .7 to .8 EC for plants that size in veg.
If your girls are eating well, you'll want to frequently change the rez. When running low ppm your rez can run short of nutes pretty quick, so top off to .8 ec and 5.8ish daily.
quit using anything with the word zyme in it. Chlorine and chloramine are not that evil, I add both to my rez. (tap water and Zone)