I would cut back from 12 net pots to 8. You are going to run into some seious space issues if you try and fit 12 girls in that little tub. Not only will the roots run out of space but your folage will be affected because it will not have any space to grow. as far as adding medium to your net pots it depends on what your using. Are you using rockwool cubes? if you are what size are they. If there is space left in the net pots ater you ad he rockwool then you DEF want some type of medium in there as well. Hydroton would work best. Good luck with everything and keep it up. But deffinetly go a little smaller. You will regret it when you hve to kill a couple of girls because of space issues.