lava and knat live and thrive in warm moist soil! i had this same problem not so long ago. the best way that i dealt with it with out using chemicals was to let the soil dry out completely for a few days and hang the bright yellow sticky fly - catch cards in the grow room. also place them face up on top of the soil as the lava that are born tend to fly out of the soil and on to the sticky card preventing them from breeding. sliced potato on top of the soil is also good as adult knats prefer to lay their eggs on them. hope this helps!!