aussie needs help

i have six plants under a son. t agro 430 they were two week old cuttings and been in my system for a week. 1 .how high should i have my light 2 .how often should i give them nutrient .the roots are starting to shoot out of the fiber blocks into the clay balls

between 12-18", or another way to tell is place ur hand under the light the same hight as the plants if u find it uncomftable move the light acordinly to suite.remember that the plants r under the lights for18-24 hours.