plant has slow growth

hey all, i have a plant ive cloned off mates plant,rooted fast and now has been under 600w hps for 6-8 weeks and hasnt got any side growth
its about 10-13'' tall new growth looks good,my question is if i re-clone it will it do better or is it a weak plant?
thanks for all in-put considering this problem

6-8 weeks and is a foot tall? something is amiss. temps?

pictures would help alot

temps are good 27-29c light on 20-23 lights out,circulating fan,light hight 18'',ph 6.2 when last checked.1/2 strenght fert,RE-CLONE it???