Grow Container/ Roots Question

okay my original grow space was in my attic but due to very ab normal temps
i decided to put them down stairs where the house maintained a temp of about 68
and with my ventilation in grow box its about 75.
Heres my thing. My plants seemed as if they just stopped growing and had me dumb founded
being this is my first grow.
They are about 3 weeks old and are in FF ocean forest.

I have them in small containers very small since seedlings.
Is this because they need a transplant?
The roots are showing. If so what would you recommend?
Size?

PS how high should you hang a 150 watt HPS light from the girls?
THANKS IN ADVANCE GUYS!

Yes if rootbound the plant stops growing and suffers moisture stress. Plus more salts build up in a small pot.