Trainwreck auto 3wks/only3"

1st grow. Using Mars hydro 3000. Started with dimmer,and have turned it up a bit. Height 30". pH at 6.5. watering about every 3 days. Running fans and AC in a 4x4 to maintain temp, and humidity. They look healthy to me, but seem awfully small. Any opinions, or advice appreciated.

Get your light about 18" from the tops.
It's a 300w light.
Get it close.

Looks good otherwise.
***edit. When I run a 250w hps is an air cooled hood its @ about 8" for reference

Thanks for the heads-up