What should my next move be??

At the moment, I have two plants. The older of the two (in pics below) is now six weeks old. I recently transplanted it into the larger container seen. Its been growing at a pretty reasonable rate from what I've read and compared it to, however the past week or so has shown alot less growth than prior to transplanting.

I guess a couple of questions rise up here...

1) Is it possible that I threw it into shock transplanting it? If so, how long does this last, and is there anything I should be doing to help it along?
2) Once growth picks up again, what should my next move be? I've been running it under a HPS bulb on an 18/6 schedule. Is it time to move to 12/12??


Thanks in advance!

Try dome transplant shock/ root stimulator solution, you can pick some up at your local ace or local department store and add it once a week for a couple weeks and this should speed up the process as well as prevent shock