Slow Growth?

Hey People,i have start a drip system about 3 and a half weeks ago i am using fox farms nutrients big bud and grow big or something like that it came in a 3 pack i got online, either way also running a 400w hps from htg supply, it is all set up in a closet covered in reflective materials, i have plenty of air circulation in there with a squirell cage fan, them temp is right and the nutes were applied as directed, my problem is i am not seeing a lot of growth, been three weeks and im just starting to see my fifth row of leaves come out and the plant only stands about 4 inches tall, nice healthy looking leaves though. also i am using perlite as my growing medium i dont know if that helps or not. please let me know what you think the problem is or if there is no problem at all and i am just to impatient. thank you all.

give it another few days to a week they shoot shoot off if condition is right.

whats the pH level is the water? have you a temp gauge for accurate temp condition?

humid level?

if you running drip system they should grow fast enough, as I use soil and they shoot off after 3 weeks. can you post some pics, it helps.