Plant stunted?

Hi, everyone recently notice my plant is just short and brush, it doesn't get taller. First time growing in 4by4 rockwool usually use 6by6 cubes. Going tranplant to 5 gallon pot need bigger plants. Is it because of a smaller cube ?
Plant looks healthy but don't seem to grow much taller. Is that bad?
First time having this problem.
Normally they should sterch by now.


Any ideas or input would be great.


Abit of info

Platinum kush strain
2 1000hps
3.9 week veg
4by4 rockwool
Flood table
Light was 2.5ft away from plant
Ppm 500-700/ 3 part AN
Ph5.7 - 6.2 range
Cal mag, superthrive
Low temp 59 hi temp 78 ish

Thanks for stopping by

They should stretch once you turn them and could expand triple the size now.

*59 is pretty low. Temps that low can slow down growth.