I usually mix up 4L of nutrient solution and keep it in the fridge and I top off my aerogardens res daily till the 4L is gone then mix up another batch nutrients. I do not have a ppm or any of that just follow a simple General Hydroponics drain to waste feed chart i got with my nutrients.
here is a few pictures taken today will be making another video tonight, as you can see my plant is super dry not sure why she has been through a lot and once i finish her and the other 3 i will be totally re setting up a new flood system but for now see what happens, started flushed today will be harvesting in one week.