I would suggest a HPS (high pressure sodium) system, my plants have been doubling in size every day sense i starting using it.

Ive herd MH ( metal halide) bulbs work better for veg growing and hps are best for budding. I got a switchable ballest so i can use both types of lights with a flip of a switch. $200 total for a good light system.
if you dont have the cash, i used Cfls for the longest time and they work, just never got the yields i wanted.

whats your light schedule? are the lights on 24 hours a day? or 18/6?

I grow hydro so i dont know much about the soil. but I would think miracle grow is fine.
can you touch your lights with out them being to hot on your hand? if so the light spacing if good.

and what is the PH of your soil, I dont know if thats a big issue for soil but with hydro Ph is one of the main keys to growing. Ph of 5.8-6.2 is best i believe.

Hope ive been a help.
happy smokes