They could be fungus gnats. I recently just had a similar problem, the soil was completely engulfed with small bugs. The mix i used was 4tbsp of gognats and a couple drops of palmolive dish soup in a gallon of water. i only ended up running this for one feeding and no problems since. this should take care of the larvae, as for the adults leave a couple of cups of beer and a small amount of dish soap around the grow. The fly's tend to be attracted to the beer, they fly right in to feed and the dish soup puts them to sleep.