Ok.....excellent. What nutes are you using? Get your CalMag, your RO water and your grow nutes together.....I personally would put my ppms at about 300 since you are starting with water at about 20. I use 150ppm CalMag and `150ppm 1 part grow nutes.

You have plants of different ages together so you'll have to be very careful about overnute/undernute. I'm honestly not sure if you can grow good plants of different ages together in hydro but IF I were going to try it I would use the 300ppms to start. You said you've been keeping your ph between 5.5 and 5.8....excellent....keep doing that. Hope this works for you but realize that you are WAY playing defense here. Good luck.