Help im a Noob and there seems to be something wrong

Hey guys i was wondering if you can help me. Im not sure but i think theres something wrong with my plants. i have 9 of them growing in with a 600w mh bulb with a 20/4 lighting. they have been going on 3 weeks and are still pretty damn small. the pics are included...im using miracle grow...should i change the soil???? im watering about every 2-3 days. I did have some problems with the temperature but it has been between 70-90 degrees and the humidity in the room did drop due to the dry cold front that hit but i got a humidifier and placed it in the room a few days ago and it has kept it at 40-50% and holding steady. They just dont seem to be groing up as fast as i thought they would during this time. Any help is greatly apriciated

how far is your light from your plants they do seem very small for 3 weeks

is that a 6500 K bulb ? if not, that's your problem.
yeah, how far away do you have the light ?
They look healthy so I don't think your problem is below the soil.

They look healthy to me also. They could be slow starters. What are the genetics?

one is a indiga and the other type is a hybrid. the light is pretty high up....i put it up high to try to dampen some of the heat when i first placed them in there cuz it was getting pretty hot but i got all that under control and will lower the light to see if that helps..

Try moving the light closer. I use MG also, my plants were around that size at 2 1/2-3 weeks, just be patient they'll take off, they look healthy.

Good luck.