Hey whats up? I am on my first grow similar to yours (600w, 4x4, soil grow) and had a fungus gnat problem from the start because the soil of the cloned plants was infested when they were given to me. They started multiplying so I got worried and got some advice from the local grow store. I put up sticky strips all over the tent and watered with Azamax (organic, soapy liquid that kills the larvae in 2-3 weeks). It is now 2 weeks later and no sign of them. The sticky strips took care of any adults and the Azamax took care of the larvae... problem solved. This is my first post hope it was helpful.