depends what kinda critter they are. if its fungus gnats they will not be much of a problem unless they are indoors, then it gets downright annoying. if its a root eating grub you gotta snuff them! best way would be to flush your soil till it runs clear then water it with a control measure of some sort that wont hurt your plants.
if it was me, i would use hydrogen peroxide, maybe 4 tablespoons in a gallon, but not that supermarket shit. its got crap in it that will kill your plant. go to a health food store and get some of the shit thats rated for drinking (but dont drink it for christ's sake, that shit is crazy stupid). Then at your next scheduled watering keep adding 1 tablespoon per gallon with your nutrients, and hope that does it.
i would ask around from the cannabis experts too, i grow vegetables mostly, not dope. they may have something thats a better fit, but you certainly want to flush that rotting wood out of there. Thats why i dont use miracle grow soil unless i compost it with worms first. Its full of whole twigs, and half composted wood and shit. plants can't use that, and when it decomposes imany types of wood make highly alkaline byproducts, and some types make surprisingly strong acids. Miracle grow is only useful after worms have eaten it for a few months.