The just don’t want you to mix the nutrients together and THEN add it to the water. Adding the nutes to your water and letting it sit around isn’t a problem. For example you have your bucket of water, you add nutes to it like I described above… totally fine.
As far as PPM, I only monitored that during flowering. I stayed with the “3-2-1” ratio for the GH 3-part (Micro/Grow/Bloom), which is basically 3 parts Bloom, 2 parts Micro, 1 part Grow/CaliMagic. To give you some real numbers:
During the late flower stage (before ripening), I was using the chart I posted above, and putting these nutrients in my water (per gallon):
That is a ratio of 2:1 Bloom to Micro.
So let’s say that I’ve added that per gallon to my water, and my PPM comes out to 700 PPM. I want to get up to 950PPM, so I will add 2ml of FloraBloom and 1ml of FloraMicro, check again, and keep doing that until I get to where I want my PPM to be.
Clear as mud? Basically once you figure out the ratios of nutrients you are adding, you can just use that ratio and add as much as needed to get PPM where you want.
That’s how I have done it, but I am at the end of my first grow, so hopefully a more experienced person will chime in.