Purple Queen (Newcomer)

Hello everybody, I am an absolute newcomer and am grateful for any advice. In my new apartment I have the opportunity to fulfill my little dream and have bought myself a homebox with suitable equipment. I have read the last weeks intensively in the topic and just hope to take with my first grow a good experience for the next attempt. Practice creates masters. I chose Royal Queen Seeds for the Purple Queen Seeds variety and planted them in suitable seedling soil. I think the result after a week is quite amazing. Now the fresh plants are under a metal halide lamp with 400 watts in my Growbox. Regrettably, a misadventure happened to me, I fell down the stairs with the small plants of my hand and in 6 out of 9 plants the main trunk is broken. I will consider the last 3 plants as an experience and try to grow. I would be grateful for any advice, special about amounts of fertilizer and amount of water from the third week. I find the topic very exciting, unfortunately I can not talk to friends or family about it. I hope to get some exchange here. Best regards Knobination